use 5.10;
my @lines = split /\s*\n/, <<"EOT";
1, 2, 5, 1, 2, 5, 1, 2, 5
3, 6, 3, 6, 3, 6, 3, 6
4, 1, 28, 0, 4, 1, 28, 0
3, 5, 17, 3, 17, 5
4, 1, 28, 0, 4, 1, 28
EOT

foreach (@lines) {
    $_ .= ", ";
    say /^(.+?)\1+$/ ? length()/length($1) : 0;
}

__END__
3
4
2
0
0