別搗蛋

1.

密碼和用戶名相同。
如：用戶名和密碼都是123456789。幾乎所有盜取密碼的人，都會以用戶名作為破解密碼的突破口。



2.

密碼為用戶名中的某幾個鄰近的數字或字母。
如：用戶名為test000001，密碼為test或000001。如果您的用戶名是字母和數字組合，如：test000001，那麼別人要盜取您的密碼時，肯定會以用戶名中的字母或數字來試密碼。



3.

密碼為連續或相同的數字。
如123456789、1111111等。幾乎所有駭客軟體，都會從連續或相同的數字開始試密碼。如：先試 111、111……到9999999999，然後再試123、321、234、1234……如果您的密碼是111111、123456或654321，甚至用不著駭客軟體也能在片刻試出。



4.

密碼為連續或相同的數字。
如abcdefg、jjjjjjj等。字母雖然比數字多，但是先試相同的字母如aaaaa，再試連續的字母如abcde，駭客軟體所用時間也不會太多。



5.

將用戶名顛倒或加前尾碼作為密碼。
如用戶名為test，密碼為test123、aaatest、tset等。以用戶名test為例，駭客軟體在嘗試使用test作為密碼之後，還會試著使用諸如test123、test1、tset、tset123等作為密碼，只要是你想得到的變換方法，駭客軟體也會想得到，它破解這種密碼，幾乎不需要時間。



6.

使用姓氏的拼音作為密碼。
在不少駭客軟體中，百家姓往往都被一一列出，並放在字典的前列。只需片刻即可破解您的密碼。以姓氏或姓名的拼音作為密碼還存在一種危險：想盜您密碼的人如果探聽到您的真實姓名，就很有可能用您姓名中的拼音組合來試密碼。



7.

使用自己或親友的生日作為密碼。
由於表示月份的只有1～12可以使用，表示日期的也只有1-31可以使用，表示日期的肯定19xx咖@@x，因此表達方式只有100×12×31×2＝74,400種，即使考慮到年月日共有六種排列順序，一共也只有74400×6＝446,400種。按普通電腦每秒搜索 3～4萬種的速度計算，破解您的密碼最多只需10秒。



8.

使用常用英文單詞作為密碼。
駭客軟體一般都有一個包含10萬～20萬個英文單詞及相應組合的字典庫。如果您的密碼在這個庫中，那麼即使字典庫中有20萬單詞，再考慮到一些DES(數據加密演算法)的加密運算，每秒搜索1,800個，也只需要110秒。



9.

使用8位以下的數字作為密碼。
數字只有10個，8位數字組成方式只有10的8次方＝100,000,000種，按普通電腦每秒搜索3～4萬種的速度計算，駭客軟體只需要不到3小時就可以破解您的密碼了。



10.

使用5位以下的小寫字母加數字作為密碼。
小寫字母加數字一共36位，組合方式只有36的5次方＝60,466,176種可能性，按普通的電腦每秒搜索3-4萬種的速度計算，駭客軟體只需要25分鐘就可以破解密碼。

#/usr/bin/perl
#二進位轉十進位
sub bin2dec {
return unpack("N", pack("B*", substr("0" x 32 . shift, -32)));
}
#十六進位轉十進位
sub hex2dec {
return unpack("N", pack("H*", substr("0" x 8 . shift, -8)));
}
#八進位轉十進位
sub oct2dec {
my $b = unpack("B*", pack("H*", substr("0" x 8 . shift, -8)));
$b =~ s/0([01]{3})/$1/g;
return bin2dec($b);
}
#十進位轉二進位
sub dec2bin {
my $b = unpack("B*", pack("N", shift));
$b =~ s/^0+//;
return $b;
}
#十六進位轉二進位
sub hex2bin {
my $b = unpack("B*", pack("H*", substr("0" x 8 . shift, -8)));
$b =~ s/^0+//;
return $b;
}
#八進位轉二​進位
sub oct2bin {
my $b = hex2bin(shift);
$b =~ s/0([01]{3})/$1/g;
$b =~ s/^0+//;
return $b;
}

#!/usr/bin/perl

# 使用遞迴方法 (recursive) - 速度慢
# 輸入 : 整數 n
# 輸出 : 費波那契數
sub fibonacci {
my $n = shift;
return 0 if ($n==0);
return 1 if ($n==1);
return fibonacci($n+2) - fibonacci($n+1) if ($n<0);
return fibonacci($n-1) + fibonacci($n-2);
}

# 使用疊代方法 (iterative) - 速度快
# 輸入 : 整數 n
# 輸出 : 費波那契數
sub fibonacci_i {
my $n = shift;
my (@fib, $i, $neg);

$neg = 0;
if ($n<0) {
$n = abs($n);
$neg = 1;
}

$fib[0] = 0;
$fib[1] = 1;
for ($i=2;$i<=$n;$i++) {
$fib[$i] = $fib[$i-1] + $fib[$i-2];
}
return (-1)**($n+1)*$fib[$n] if ($neg);
return $fib[$n];
}

# sort 預設使用字母順序升冪排序
@articles = sort @files;

# 同上，使用字母順序升冪排序
@articles = sort {$a cmp $b} @files;

# 同上，使用字母順序降冪排序
@articles = sort {$b cmp $a} @files;
@articles = reverse sort @files;

# 使用數字順序升冪排序
@articles = sort {$a <=> $b} @files;

# 使用數字順序降冪排序
@articles = sort {$b <=> $a} @files;

# 不分大小寫字母順序排序
@articles = sort {uc($a) cmp uc($b)} @files;
@articles = sort {lc($a) cmp lc($b)} @files;

# 使用字串長度順序排序
@articles = sort {lenth($a) <=> length($b)} @files;

# 使用字串長度與字母順序排序
@articles = sort {lenth($a) <=> length($b) || $a cmp $b} @files;

# %age雜湊值降冪排序
@eldest = sort { $age{$b} <=> $age{$a} } keys %age;

O'Reilly CD 書架
Developer.com

$pi = 4 * atan2(1, 1);

$e = exp(1);

sub floor { $_[0]<0 ? int($_[0]-.999999999999999) : int($_[0]) }

sub ceil { $_[0]<0 ? int($_[0]) : int($_[0]+.999999999999999) }

sub round { int($_[0] + .5*($_[0] <=> 0)) }

sub deg2rad { $_[0] * $pi / 180 }

sub rad2deg { $_[0] * 180 / $pi }

sub tan { sin($_[0]) / cos($_[0]) }

sub cot { cos($_[0]) / sin($_[0]) }

sub sec { 1 / cos($_[0]) }

sub csc { 1 / sin($_[0]) }

sub atan { atan2($_[0], 1) }

sub asin { abs($_[0])>1 ? undef : atan2($_[0], sqrt(1 - $_[0]*$_[0])) }

sub acos { abs($_[0])>1 ? undef : atan2(sqrt(1 - $_[0]*$_[0]), $_[0]) }

sub sinh { (exp($_[0]) - exp(-$_[0])) / 2 }

sub cosh { (exp($_[0]) + exp(-$_[0])) / 2 }

sub tanh { (exp(2*$_[0])-1) / (exp(2*$_[0])+1) }

sub asinh { log($_[0] + sqrt($_[0]*$_[0] + 1)) }

sub acosh { $_[0]<1 ? undef : log($_[0] + sqrt($_[0]*$_[0] - 1)) }

sub atanh { abs($_[0])>1 ? undef : log((1 + $_[0])/(1 - $_[0])) / 2 }

sub log10 { log($_[0]) / log(10) }

#!/usr/bin/perl

# 使用遞迴方法 (recursive)
# 輸入 : 正整數 n
# 輸出 : 階乘 n!
sub factorial {
my $n = shift;

return 'NaN' if ($n<0);
return 1 if ($n<2);
return $n*factorial($n-1);
}

# 使用疊代方法 (iterative)
# 輸入 : 正整數 n
# 輸出 : 階乘 n!
sub factorial_i {
my $n = shift;
my $fact = 1;

return 'NaN' if ($n<0);
while ($n>1) {
$fact *= $n;
$n = $n - 1;
}
return $fact;
}

#!/usr/bin/perl

# 輸入 : 正整數 n
# 輸出 : 小於 n 之完全數
sub perfect {
my $n = shift;
my ($c, $i);

$c = 1;
for $i (1..$n) {
if (is_perfect($i)==1) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n 之盈數
sub abundant {
my $n = shift;
my ($c, $i);

$c = 1;
for $i (1..$n) {
if (is_perfect($i)==2) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n 之虧數
sub deficient {
my $n = shift;
my ($c, $i);

$c = 1;
for $i (1..$n) {
if (is_perfect($i)==3) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

---

Character
  HTML Entity
Description


Number
Name

---

"
&#34;
&quot;
quotation mark



&
&#38;
&amp;
ampersand



'
&#39;
&apos;
apostrophe / apostrophe-quote



<
&#60;
&lt;
less-than sign



>
&#62;
&gt;
greater-than sign



 
&#160;
&nbsp;
no-break space / non-breaking space



¡
&#161;
&iexcl;
inverted exclamation mark



¢
&#162;
&cent;
cent sign



£
&#163;
&pound;
pound sign



¤
&#164;
&curren;
currency sign



¥
&#165;
&yen;
yen sign



¦
&#166;
&brvbar;
broken bar / broken vertical bar



§
&#167;
&sect;
section sign



¨
&#168;
&uml;
diaeresis / spacing diaeresis / umlaut



©
&#169;
&copy;
copyright sign



ª
&#170;
&ordf;
feminine ordinal indicator



«
&#171;
&laquo;
left-pointing double angle quotation mark



¬
&#172;
&not;
not sign



­
&#173;
&shy;
soft hyphen / discretionary hyphen



®
&#174;
&reg;
registered sign / registered trademark sign



¯
&#175;
&macr;
macron / spacing macron/ overline



°
&#176;
&deg;
degree sign



±
&#177;
&plusmn;
plus-minus sign / plus-or-minus sign



²
&#178;
&sup2;
superscript two / superscript digit two / squared



³
&#179;
&sup3;
superscript three / superscript digit three / cubed



´
&#180;
&acute;
acute accent / spacing acute



µ
&#181;
&micro;
micro sign



¶
&#182;
&para;
pilcrow sign / paragraph sign



·
&#183;
&middot;
middle dot / Georgian comma / Greek middle dot



¸
&#184;
&cedil;
cedilla / spacing cedilla



¹
&#185;
&sup1;
superscript one / superscript digit one



º
&#186;
&ordm;
masculine ordinal indicator



»
&#187;
&raquo;
right-pointing double angle quotation mark



¼
&#188;
&frac14;
fraction one quarter



½
&#189;
&frac12;
fraction one half



¾
&#190;
&frac34;
fraction three quarters



¿
&#191;
&iquest;
inverted question mark / turned question mark



À
&#192;
&Agrave;
Latin capital letter A with grave



Á
&#193;
&Aacute;
Latin capital letter A with acute



Â
&#194;
&Acirc;
Latin capital letter A with circumflex



Ã
&#195;
&Atilde;
Latin capital letter A with tilde



Ä
&#196;
&Auml;
Latin capital letter A with diaeresis



Å
&#197;
&Aring;
Latin capital letter A with ring above



Æ
&#198;
&AElig;
Latin capital letter AE / Latin capital ligature AE



Ç
&#199;
&Ccedil;
Latin capital letter C with cedilla



È
&#200;
&Egrave;
Latin capital letter E with grave



É
&#201;
&Eacute;
Latin capital letter E with acute



Ê
&#202;
&Ecirc;
Latin capital letter E with circumflex



Ë
&#203;
&Euml;
Latin capital letter E with diaeresis



Ì
&#204;
&Igrave;
Latin capital letter I with grave



Í
&#205;
&Iacute;
Latin capital letter I with acute



Î
&#206;
&Icirc;
Latin capital letter I with circumflex



Ï
&#207;
&Iuml;
Latin capital letter I with diaeresis



Ð
&#208;
&ETH;
Latin capital letter ETH



Ñ
&#209;
&Ntilde;
Latin capital letter N with tilde



Ò
&#210;
&Ograve;
Latin capital letter O with grave



Ó
&#211;
&Oacute;
Latin capital letter O with acute



Ô
&#212;
&Ocirc;
Latin capital letter O with circumflex



Õ
&#213;
&Otilde;
Latin capital letter O with tilde



Ö
&#214;
&Ouml;
Latin capital letter O with diaeresis



×
&#215;
&times;
multiplication sign



Ø
&#216;
&Oslash;
Latin capital letter O with stroke / slash



Ù
&#217;
&Ugrave;
Latin capital letter U with grave



Ú
&#218;
&Uacute;
Latin capital letter U with acute



Û
&#219;
&Ucirc;
Latin capital letter U with circumflex



Ü
&#220;
&Uuml;
Latin capital letter U with diaeresis



Ý
&#221;
&Yacute;
Latin capital letter Y with acute



Þ
&#222;
&THORN;
Latin capital letter THORN



ß
&#223;
&szlig;
Latin small letter sharp s / ess-zed



à
&#224;
&agrave;
Latin small letter a with grave



á
&#225;
&aacute;
Latin small letter a with acute



â
&#226;
&acirc;
Latin small letter a with circumflex



ã
&#227;
&atilde;
Latin small letter a with tilde



ä
&#228;
&auml;
Latin small letter a with diaeresis



å
&#229;
&aring;
Latin small letter a with ring above



æ
&#230;
&aelig;
Latin small letter ae / Latin small ligature ae



ç
&#231;
&ccedil;
Latin small letter c with cedilla



è
&#232;
&egrave;
Latin small letter e with grave



é
&#233;
&eacute;
Latin small letter e with acute



ê
&#234;
&ecirc;
Latin small letter e with circumflex



ë
&#235;
&euml;
Latin small letter e with diaeresis



ì
&#236;
&igrave;
Latin small letter i with grave



í
&#237;
&iacute;
Latin small letter i with acute



î
&#238;
&icirc;
Latin small letter i with circumflex



ï
&#239;
&iuml;
Latin small letter i with diaeresis



ð
&#240;
&eth;
Latin small letter eth



ñ
&#241;
&ntilde;
Latin small letter n with tilde



ò
&#242;
&ograve;
Latin small letter o with grave



ó
&#243;
&oacute;
Latin small letter o with acute



ô
&#244;
&ocirc;
Latin small letter o with circumflex



õ
&#245;
&otilde;
Latin small letter o with tilde



ö
&#246;
&ouml;
Latin small letter o with diaeresis



÷
&#247;
&divide;
division sign / obelus



ø
&#248;
&oslash;
Latin small letter o with stroke / slash



ù
&#249;
&ugrave;
Latin small letter u with grave



ú
&#250;
&uacute;
Latin small letter u with acute



û
&#251;
&ucirc;
Latin small letter u with circumflex



ü
&#252;
&uuml;
Latin small letter u with diaeresis



ý
&#253;
&yacute;
Latin small letter y with acute



þ
&#254;
&thorn;
Latin small letter thorn



ÿ
&#255;
&yuml;
Latin small letter y with diaeresis



Œ
&#338;
&OElig;
Latin capital ligature oe



œ
&#339;
&oelig;
Latin small ligature oe



Š
&#352;
&Scaron;
Latin capital letter s with caron



š
&#353;
&scaron;
Latin small letter s with caron



Ÿ
&#376;
&Yuml;
Latin capital letter y with diaeresis



ƒ
&#402;
&fnof;
Latin small letter f with hook / function / florin



ˆ
&#710;
&circ;
modifier letter circumflex accent



˜
&#732;
&tilde;
small tilde



Α
&#913;
&Alpha;
Greek capital letter Alpha



Β
&#914;
&Beta;
Greek capital letter Beta



Γ
&#915;
&Gamma;
Greek capital letter Gamma



Δ
&#916;
&Delta;
Greek capital letter Delta



Ε
&#917;
&Epsilon;
Greek capital letter Epsilon



Ζ
&#918;
&Zeta;
Greek capital letter Zeta



Η
&#919;
&Eta;
Greek capital letter Eta



Θ
&#920;
&Theta;
Greek capital letter Theta



Ι
&#921;
&Iota;
Greek capital letter Iota



Κ
&#922;
&Kappa;
Greek capital letter Kappa



Λ
&#923;
&Lambda;
Greek capital letter Lambda



Μ
&#924;
&Mu;
Greek capital letter Mu



Ν
&#925;
&Nu;
Greek capital letter Nu



Ξ
&#926;
&Xi;
Greek capital letter Xi



Ο
&#927;
&Omicron;
Greek capital letter Omicron



Π
&#928;
&Pi;
Greek capital letter Pi



Ρ
&#929;
&Rho;
Greek capital letter Rho



Σ
&#931;
&Sigma;
Greek capital letter Sigma



Τ
&#932;
&Tau;
Greek capital letter Tau



Υ
&#933;
&Upsilon;
Greek capital letter Upsilon



Φ
&#934;
&Phi;
Greek capital letter Phi



Χ
&#935;
&Chi;
Greek capital letter Chi



Ψ
&#936;
&Psi;
Greek capital letter Psi



Ω
&#937;
&Omega;
Greek capital letter Omega



α
&#945;
&alpha;
Greek small letter alpha



β
&#946;
&beta;
Greek small letter beta



γ
&#947;
&gamma;
Greek small letter gamma



δ
&#948;
&delta;
Greek small letter delta



ε
&#949;
&epsilon;
Greek small letter epsilon



ζ
&#950;
&zeta;
Greek small letter zeta



η
&#951;
&eta;
Greek small letter eta



θ
&#952;
&theta;
Greek small letter theta



ι
&#953;
&iota;
Greek small letter iota



κ
&#954;
&kappa;
Greek small letter kappa



λ
&#955;
&lambda;
Greek small letter lambda



μ
&#956;
&mu;
Greek small letter mu



ν
&#957;
&nu;
Greek small letter nu



ξ
&#958;
&xi;
Greek small letter xi



ο
&#959;
&omicron;
Greek small letter omicron



π
&#960;
&pi;
Greek small letter pi



ρ
&#961;
&rho;
Greek small letter rho



ς
&#962;
&sigmaf;
Greek small letter final sigma



σ
&#963;
&sigma;
Greek small letter sigma



τ
&#964;
&tau;
Greek small letter tau



υ
&#965;
&upsilon;
Greek small letter upsilon



φ
&#966;
&phi;
Greek small letter phi



χ
&#967;
&chi;
Greek small letter chi



ψ
&#968;
&psi;
Greek small letter psi



ω
&#969;
&omega;
Greek small letter omega



ϑ
&#977;
&thetasym;
Greek theta symbol



ϒ
&#978;
&upsih;
Greek Upsilon with hook symbol



ϖ
&#982;
&piv;
Greek pi symbol



 
&#8194;
&ensp;
en space



 
&#8195;
&emsp;
em space



 
&#8201;
&thinsp;
thin space



‌
&#8204;
&zwnj;
zero-width non-joiner



‍
&#8205;
&zwj;
zero-width joiner



‎
&#8206;
&lrm;
left-to-right mark



‏
&#8207;
&rlm;
right-to-left mark



–
&#8211;
&ndash;
en dash



—
&#8212;
&mdash;
em dash



‘
&#8216;
&lsquo;
left single quotation mark



’
&#8217;
&rsquo;
right single quotation mark



‚
&#8218;
&sbquo;
single low-9 quotation mark



“
&#8220;
&ldquo;
left double quotation mark



”
&#8221;
&rdquo;
right double quotation mark



„
&#8222;
&bdquo;
double low-9 quotation mark



†
&#8224;
&dagger;
dagger, obelisk



‡
&#8225;
&Dagger;
double dagger, double obelisk



•
&#8226;
&bull;
bullet / black small circle



…
&#8230;
&hellip;
horizontal ellipsis / three dot leader



‰
&#8240;
&permil;
per mille sign



′
&#8242;
&prime;
prime / minutes / feet



″
&#8243;
&Prime;
double prime / seconds / inches



‹
&#8249;
&lsaquo;
single left-pointing angle quotation mark



›
&#8250;
&rsaquo;
single right-pointing angle quotation mark



‾
&#8254;
&oline;
overline / spacing overscore



⁄
&#8260;
&frasl;
fraction slash / solidus



€
&#8364;
&euro;
euro sign



ℑ
&#8465;
&image;
black-letter capital I / imaginary part



℘
&#8472;
&weierp;
script capital P / power set / Weierstrass p



ℜ
&#8476;
&real;
black-letter capital R / real part symbol



™
&#8482;
&trade;
trademark sign



ℵ
&#8501;
&alefsym;
alef symbol / first transfinite cardinal



←
&#8592;
&larr;
leftwards arrow



↑
&#8593;
&uarr;
upwards arrow



→
&#8594;
&rarr;
rightwards arrow



↓
&#8595;
&darr;
downwards arrow



↔
&#8596;
&harr;
left right arrow



↵
&#8629;
&crarr;
downwards arrow with corner leftwards



⇐
&#8656;
&lArr;
leftwards double arrow



⇑
&#8657;
&uArr;
upwards double arrow



⇒
&#8658;
&rArr;
rightwards double arrow



⇓
&#8659;
&dArr;
downwards double arrow



⇔
&#8660;
&hArr;
left right double arrow



∀
&#8704;
&forall;
for all



∂
&#8706;
&part;
partial differential



∃
&#8707;
&exist;
there exists



∅
&#8709;
&empty;
empty set / null set / diameter



∇
&#8711;
&nabla;
nabla / backward difference



∈
&#8712;
&isin;
element of



∉
&#8713;
&notin;
not an element of



∋
&#8715;
&ni;
contains as member



∏
&#8719;
&prod;
n-ary product / product sign



∑
&#8721;
&sum;
n-ary summation



−
&#8722;
&minus;
minus sign



∗
&#8727;
&lowast;
asterisk operator



√
&#8730;
&radic;
square root / radical sign



∝
&#8733;
&prop;
proportional to



∞
&#8734;
&infin;
infinity



∠
&#8736;
&ang;
angle



∧
&#8743;
&and;
logical and / wedge



∨
&#8744;
&or;
logical or / vee



∩
&#8745;
&cap;
intersection / cap



∪
&#8746;
&cup;
union / cup



∫
&#8747;
&int;
integral



∴
&#8756;
&there4;
therefore



∼
&#8764;
&sim;
tilde operator / varies with / similar to



≅
&#8773;
&cong;
congruent to



≈
&#8776;
&asymp;
almost equal to / asymptotic to



≠
&#8800;
&ne;
not equal to



≡
&#8801;
&equiv;
identical to / equivalent to



≤
&#8804;
&le;
less-than or equal to



≥
&#8805;
&ge;
greater-than or equal to



⊂
&#8834;
&sub;
subset of



⊃
&#8835;
&sup;
superset of



⊄
&#8836;
&nsub;
not a subset of



⊆
&#8838;
&sube;
subset of or equal to



⊇
&#8839;
&supe;
superset of or equal to



⊕
&#8853;
&oplus;
circled plus / direct sum



⊗
&#8855;
&otimes;
circled times / vector product



⊥
&#8869;
&perp;
up tack / orthogonal to / perpendicular



⋅
&#8901;
&sdot;
dot operator



⌈
&#8968;
&lceil;
left ceiling



⌉
&#8969;
&rceil;
right ceiling



⌊
&#8970;
&lfloor;
left floor



⌋
&#8971;
&rfloor;
right floor



◊
&#9674;
&loz;
lozenge



♠
&#9824;
&spades;
black spade suit



♣
&#9827;
&clubs;
black club suit / shamrock



♥
&#9829;
&hearts;
black heart suit / valentine



♦
&#9830;
&diams;
black diamond suit



⟨
&#10216;
&lang;
mathematical left angle bracket / bra



⟩
&#10217;
&rang;
mathematical right angle bracket / ket

---

#!/usr/bin/perl

# 輸入 : 正整數 n
# 輸出 : 小於 n 的質數
sub prime {
my $n = shift;
my ($c, $i);

$c = 1;
for $i (2..$n) {
if (is_prime($i)) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n 的反質數
sub emirp {
my $n = shift;
my ($c, $i, $j);

$c = 1;
for $i (2..$n) {
$j = reverse $i;
if (is_prime($i) && is_prime($j) && !($i==$j)) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n 的迴文質數
sub palprime {
my $n = shift;
my ($c, $i, $j);

$c = 1;
for $i (2..$n) {
$j = reverse $i;
if ($i==$j && is_prime($i)) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n+2 的孿生質數
sub twin_prime {
my $n = shift;
my ($c, $i, $j);

$c = 1;
for $i (2..$n) {
if (is_prime($i) && is_prime($i+2)) {
printf "%d %d %d\n", $c, $i, $i+2;
$c++;
}
}
}

# 輸入 : 正整數 n
# 輸出 : 小於 n 的半質數
sub semiprime {
my $n = shift;
my ($c, $i);

$c = 1;
for $i (2..$n) {
if (is_semiprime($i)) {
printf "%d %d\n", $c, $i;
$c++;
}
}
}