a(n) = n*(1+n^2)*((2+n^2)^2-n^2)/16.

Terms

a(0) =1a(1) =20a(2) =210a(3) =1309a(4) =5720a(5) =19536a(6) =55825a(7) =139490a(8) =314019a(9) =650440a(10) =1258796a(11) =2302455a(12) =4015570a(13) =6724004a(14) =10870035a(15) =17041156a(16) =26003285a(17) =38738700a(18) =56489014a(19) =80803505a(20) =113593116a(21) =157190440a(22) =214416005a(23) =288651174a(24) =383917975a(25) =504966176a(26) =657367920a(27) =847620235a(28) =1083255734