40*n^2 + 9 is a square.

Terms

a(0) =0a(1) =1a(2) =2a(3) =9a(4) =40a(5) =77a(6) =342a(7) =1519a(8) =2924a(9) =12987a(10) =57682a(11) =111035a(12) =493164a(13) =2190397a(14) =4216406a(15) =18727245a(16) =83177404a(17) =160112393a(18) =711142146a(19) =3158550955a(20) =6080054528a(21) =27004674303a(22) =119941758886a(23) =230881959671