Numbers k such that the concatenation of k with 4*k gives a square.

Terms

a(0) =25721a(1) =28836a(2) =32129a(3) =35600a(4) =39249a(5) =43076a(6) =47081a(7) =51264a(8) =55625a(9) =60164a(10) =64881a(11) =69776a(12) =74849a(13) =80100a(14) =85529a(15) =91136a(16) =96921a(17) =102884a(18) =109025a(19) =115344a(20) =121841a(21) =128516a(22) =135369a(23) =142400a(24) =149609a(25) =156996a(26) =164561a(27) =172304a(28) =180225a(29) =188324