a(n) = floor(n(n+2)(2n+1)/8).

Terms

a(0) =0a(1) =1a(2) =5a(3) =13a(4) =27a(5) =48a(6) =78a(7) =118a(8) =170a(9) =235a(10) =315a(11) =411a(12) =525a(13) =658a(14) =812a(15) =988a(16) =1188a(17) =1413a(18) =1665a(19) =1945a(20) =2255a(21) =2596a(22) =2970a(23) =3378a(24) =3822a(25) =4303a(26) =4823a(27) =5383a(28) =5985a(29) =6630