a(n) = (2*n - 1)*(7*n^2 - 7*n + 3)/3.

Terms

a(0) =1a(1) =17a(2) =75a(3) =203a(4) =429a(5) =781a(6) =1287a(7) =1975a(8) =2873a(9) =4009a(10) =5411a(11) =7107a(12) =9125a(13) =11493a(14) =14239a(15) =17391a(16) =20977a(17) =25025a(18) =29563a(19) =34619a(20) =40221a(21) =46397a(22) =53175a(23) =60583a(24) =68649a(25) =77401a(26) =86867a(27) =97075a(28) =108053a(29) =119829