a(n) = (n-1)*n*(n+1)*(n+2)*(2*n+1)/40.

Terms

a(0) =0a(1) =0a(2) =3a(3) =21a(4) =81a(5) =231a(6) =546a(7) =1134a(8) =2142a(9) =3762a(10) =6237a(11) =9867a(12) =15015a(13) =22113a(14) =31668a(15) =44268a(16) =60588a(17) =81396a(18) =107559a(19) =140049a(20) =179949a(21) =228459a(22) =286902a(23) =356730a(24) =439530a(25) =537030a(26) =651105a(27) =783783a(28) =937251a(29) =1113861