### comment on

 Need Help??
Here's a piece of code that finds all Vampire numbers with factors smaller than the argument given:
#!/usr/bin/perl use strict; use warnings 'all'; my @vampire; foreach my \$s (1 .. shift) { LOOP: foreach my \$t (1 .. \$s) { my \$prod = \$s * \$t; my \$cat = "\$s\$t"; foreach my \$d (0 .. 9) { next LOOP unless eval "\\$prod =~ y/\$d/\$d/ == \\$cat =~ y/\$d/\$d/"; } push @vampire => [\$prod, \$s, \$t]; } } @vampire = sort {\$a -> [0] <=> \$b -> [0]} @vampire; foreach my \$vamp (@vampire) { printf "%4d * %4d = %8d\n" => @\$vamp [1, 2, 0]; }

Note that if there is one vampire number (and there is), then we have an infinite number of vampire numbers. Proof: Suppose V = n * m is a vampire number. Then 10 * V = (10 * n) * m is a vampire number as well. qed.

Abigail

Here are the vampire numbers with factors smaller than 100:
21 *    6 =      126
51 *    3 =      153
86 *    8 =      688
60 *   21 =     1260
93 *   15 =     1395
41 *   35 =     1435
51 *   30 =     1530
87 *   21 =     1827
81 *   27 =     2187
86 *   80 =     6880

In reply to Re: Vampire Numbers by Abigail-II
in thread Vampire Numbers by YuckFoo

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.

Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others studying the Monastery: (3)
As of 2023-02-07 18:50 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?