my @a = (
    [2,5,10,5,12,6,21,5,10,12,23],
    [5,6,11,10,5,10,6,21,5,1,9],
    [6,5,10,15,21]
  );
  my($m, $n) = (2, 2);
  my $joined = join ';', map join(',', @$_), @a;

  while ($joined =~ /
    \b
    (?=
      ( @{[ join ',', ('\d+') x $n ]} )
      \b
      @{[ '(?> .*? \b \1 \b )' x ($m - 1) ]}
    )
  /xg) {
    print "($1)\n" unless $seen{$1}++;
  }