a(n) = n*(n+1)*(8*n + 1)/6.

Terms

a(0) =0a(1) =3a(2) =17a(3) =50a(4) =110a(5) =205a(6) =343a(7) =532a(8) =780a(9) =1095a(10) =1485a(11) =1958a(12) =2522a(13) =3185a(14) =3955a(15) =4840a(16) =5848a(17) =6987a(18) =8265a(19) =9690a(20) =11270a(21) =13013a(22) =14927a(23) =17020a(24) =19300a(25) =21775a(26) =24453a(27) =27342a(28) =30450a(29) =33785