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

Terms

a(0) =0a(1) =5a(2) =27a(3) =78a(4) =170a(5) =315a(6) =525a(7) =812a(8) =1188a(9) =1665a(10) =2255a(11) =2970a(12) =3822a(13) =4823a(14) =5985a(15) =7320a(16) =8840a(17) =10557a(18) =12483a(19) =14630a(20) =17010a(21) =19635a(22) =22517a(23) =25668a(24) =29100a(25) =32825a(26) =36855a(27) =41202a(28) =45878a(29) =50895