use strict;
use warnings;

my $string = 'ATATGCGCAT';

for my $num (0 .. 2**11 - 1) {
  print "$num: ",
    join('',
      map { substr($string, $_, 1) . ($num & (2**(9 - $_)) ? '2' : '1'); }
      0 .. 9
    ), "\n";
}

##</code><code>##

2039: A2T2A2T2G2C2G1C2A2T2
2040: A2T2A2T2G2C2G2C1A1T1
2041: A2T2A2T2G2C2G2C1A1T2
2042: A2T2A2T2G2C2G2C1A2T1
2043: A2T2A2T2G2C2G2C1A2T2
2044: A2T2A2T2G2C2G2C2A1T1
2045: A2T2A2T2G2C2G2C2A1T2
2046: A2T2A2T2G2C2G2C2A2T1
2047: A2T2A2T2G2C2G2C2A2T2