a(n) = (n^6 + 2n^5 + 2n^4 + n^3 + 2n)/2.

Terms

a(0) =4a(1) =86a(2) =705a(3) =3364a(4) =11630a(5) =32514a(6) =78211a(7) =168200a(8) =331704a(9) =610510a(10) =1062149a(11) =1763436a(12) =2814370a(13) =4342394a(14) =6507015a(15) =9504784a(16) =13574636a(17) =19003590a(18) =26132809a(19) =35364020a(20) =47166294a(21) =62083186a(22) =80740235a(23) =103852824a(24) =132234400a(25) =166805054a(26) =208600461