The index of the least n-gonal number greater than 1 that is also square, or 0 if none exists.

Terms

a(0) =8a(1) =2a(2) =81a(3) =25a(4) =6a(5) =9a(6) =2a(7) =0a(8) =7a(9) =4a(10) =3a(11) =9a(12) =22a(13) =2a(14) =49a(15) =4a(16) =8a(17) =0a(18) =17a(19) =9a(20) =81a(21) =5a(22) =2a(23) =25a(24) =46a(25) =3a(26) =10a(27) =121a(28) =6a(29) =9