perl -e '@a=qw(g a t c g a t c g a t c); for(1..1000000){$x=int(1000*rand());$s.=$a[$x]} while($s=~/(?<repeat>\w{3,})\w*\g{repeat}/g){ $m=$+{repeat};$c=()=$s=~/$m/;print "$m : $c\n"}'
gcacgt : 1
cga : 1
tggg : 1
ttg : 1
tta : 1
cct : 1