a(n) = (7*n^5+5*n^3)/12.

Terms

a(0) =0a(1) =1a(2) =22a(3) =153a(4) =624a(5) =1875a(6) =4626a(7) =9947a(8) =19328a(9) =34749a(10) =58750a(11) =94501a(12) =145872a(13) =217503a(14) =314874a(15) =444375a(16) =613376a(17) =830297a(18) =1104678a(19) =1447249a(20) =1870000a(21) =2386251a(22) =3010722a(23) =3759603a(24) =4650624a(25) =5703125a(26) =6938126a(27) =8378397a(28) =10048528a(29) =11974999