Numbers k such that the concatenation k21 is a square.

Terms

a(0) =1a(1) =15a(2) =37a(3) =79a(4) =123a(5) =193a(6) =259a(7) =357a(8) =445a(9) =571a(10) =681a(11) =835a(12) =967a(13) =1149a(14) =1303a(15) =1513a(16) =1689a(17) =1927a(18) =2125a(19) =2391a(20) =2611a(21) =2905a(22) =3147a(23) =3469a(24) =3733a(25) =4083a(26) =4369a(27) =4747a(28) =5055a(29) =5461