Dear SeqFans, Is 1_66666_5 (numbers with arbitrary number, k, of 6's, between 1 and 5, including 15 with zero 6's) the only pattern whose square uses only digits prime: 2_77777_222222_5 => 2_(k 7's)_((k+1) 2's)_5? k = 0 : 15^2 = 225 k = 1 : 165^2 = 27225 k = 2 : 1665^2 = 2772225, etc thx, zak