n*(n+1)*(n+2)*(n+3)*(20*n^2+72*n+43)/360.

Terms

a(0) =0a(1) =9a(2) =89a(3) =439a(4) =1519a(5) =4214a(6) =10038a(7) =21378a(8) =41778a(9) =76263a(10) =131703a(11) =217217a(12) =344617a(13) =528892a(14) =788732a(15) =1147092a(16) =1631796a(17) =2276181a(18) =3119781a(19) =4209051a(20) =5598131a(21) =7349650a(22) =9535570a(23) =12238070a(24) =15550470a(25) =19578195a(26) =24439779a(27) =30267909a(28) =37210509a(29) =45431864