Indices of square numbers which are also 9-gonal.

Terms

a(0) =1a(1) =3a(2) =33a(3) =91a(4) =989a(5) =2727a(6) =29637a(7) =81719a(8) =888121a(9) =2448843a(10) =26613993a(11) =73383571a(12) =797531669a(13) =2199058287a(14) =23899336077a(15) =65898365039a(16) =716182550641