genea
look and say
quines
rat
robump
self-similar
song history
string synth
stroids
tm interpreter
Unless otherwise stated, all original content on this site is licensed under your choice of the GNU FDL or the Creative Commons ShareAlike License.
Hopefully, this website is valid. You can check the XHTML, the CSS, and the RSS.
I've been informed of an extremely clever primality test implemented as a perl regular expression. Try it yourself:
perl -e 'print "$num is prime.\n" if (1 x ($num = shift)) !~ /^(11+)\1+$/' 19
perl -e 'print "$num is prime.\n" if (1 x ($num = shift)) !~ /^(11+)\1+$/' 21
It is horribly exponential and segfaults perl 5.8.0 on my system if you give it a large number. Nevertheless, it is really cool. It works by representing the number in unary, then seeing if it can be divided into two or more equal groups of two or more characters.