a(n) = (n+1)^2 * (n+2)^2 * (2*n+3) / 12.

Terms

a(0) =1a(1) =15a(2) =84a(3) =300a(4) =825a(5) =1911a(6) =3920a(7) =7344a(8) =12825a(9) =21175a(10) =33396a(11) =50700a(12) =74529a(13) =106575a(14) =148800a(15) =203456a(16) =273105a(17) =360639a(18) =469300a(19) =602700a(20) =764841a(21) =960135a(22) =1193424a(23) =1470000a(24) =1795625a(25) =2176551a(26) =2619540a(27) =3131884a(28) =3721425a(29) =4396575