a(n) = n*(n + 1)*(7*n + 11)/6.

Terms

a(0) =0a(1) =6a(2) =25a(3) =64a(4) =130a(5) =230a(6) =371a(7) =560a(8) =804a(9) =1110a(10) =1485a(11) =1936a(12) =2470a(13) =3094a(14) =3815a(15) =4640a(16) =5576a(17) =6630a(18) =7809a(19) =9120a(20) =10570a(21) =12166a(22) =13915a(23) =15824a(24) =17900a(25) =20150a(26) =22581a(27) =25200a(28) =28014a(29) =31030