a(n) = n*(2*n + 1)*(4*n + 1)/3.

Terms

a(0) =0a(1) =5a(2) =30a(3) =91a(4) =204a(5) =385a(6) =650a(7) =1015a(8) =1496a(9) =2109a(10) =2870a(11) =3795a(12) =4900a(13) =6201a(14) =7714a(15) =9455a(16) =11440a(17) =13685a(18) =16206a(19) =19019a(20) =22140a(21) =25585a(22) =29370a(23) =33511a(24) =38024a(25) =42925a(26) =48230a(27) =53955a(28) =60116a(29) =66729