Numbers k such that k*(k+1)/2 + 1 is a square.

Terms

a(0) =0a(1) =2a(2) =5a(3) =15a(4) =32a(5) =90a(6) =189a(7) =527a(8) =1104a(9) =3074a(10) =6437a(11) =17919a(12) =37520a(13) =104442a(14) =218685a(15) =608735a(16) =1274592a(17) =3547970a(18) =7428869a(19) =20679087a(20) =43298624a(21) =120526554a(22) =252362877a(23) =702480239a(24) =1470878640a(25) =4094354882a(26) =8572908965a(27) =23863649055a(28) =49966575152