a(n) = n*(n + 1)*(16*n - 1)/6.

Terms

a(0) =0a(1) =5a(2) =31a(3) =94a(4) =210a(5) =395a(6) =665a(7) =1036a(8) =1524a(9) =2145a(10) =2915a(11) =3850a(12) =4966a(13) =6279a(14) =7805a(15) =9560a(16) =11560a(17) =13821a(18) =16359a(19) =19190a(20) =22330a(21) =25795a(22) =29601a(23) =33764a(24) =38300a(25) =43225a(26) =48555a(27) =54306a(28) =60494a(29) =67135