Q = 2,7,4,5,11,8,9,17,16,12,14,13,22,22,18, 20,19,31,30,29,24,27,26,25,39,38,37,32,35,34,33,... Hello SeqFans, a(n)+ [the a(n)th term of Q] is a square. Q was always extended with the smallest available integer not yet present and not leading to a contradiction. Best, É.