a(n) = n*(7*n - 5)*(49*n^2 - 35*n - 10)/8.

Terms

a(0) =0a(1) =1a(2) =261a(3) =1956a(4) =7291a(5) =19500a(6) =42846a(7) =82621a(8) =145146a(9) =237771a(10) =368875a(11) =547866a(12) =785181a(13) =1092286a(14) =1481676a(15) =1966875a(16) =2562436a(17) =3283941a(18) =4148001a(19) =5172256a(20) =6375375a(21) =7777056a(22) =9398026a(23) =11260041a(24) =13385886a(25) =15799375a(26) =18525351a(27) =21589686a(28) =25019281a(29) =28842066