a(n) = (n+1)*(n+2)*(61*n^4 + 366*n^3 + 845*n^2 + 888*n + 360)/720.

Terms

a(0) =1a(1) =21a(2) =157a(3) =707a(4) =2353a(5) =6405a(6) =15106a(7) =31998a(8) =62349a(9) =113641a(10) =196119a(11) =323401a(12) =513149a(13) =787801a(14) =1175364a(15) =1710268a(16) =2434281a(17) =3397485a(18) =4659313a(19) =6289647a(20) =8369977a(21) =10994621a(22) =14272006a(23) =18326010a(24) =23297365a(25) =29345121a(26) =36648171a(27) =45406837