a(n) = n*(n+1)^2*(6*n^3-5*n^2+3*n+2)/24.

Terms

a(0) =0a(1) =1a(2) =27a(3) =256a(4) =1325a(5) =4815a(6) =13916a(7) =34272a(8) =75006a(9) =149925a(10) =278905a(11) =489456a(12) =818467a(13) =1314131a(14) =2038050a(15) =3067520a(16) =4497996a(17) =6445737a(18) =9050631a(19) =12479200a(20) =16927785a(21) =22625911a(22) =29839832a(23) =38876256a(24) =50086250a(25) =63869325a(26) =80677701a(27) =101020752a(28) =125469631a(29) =154662075