a(n) = Sum_{1 <= i < j <= n} j^5*i^5.

Terms

a(0) =0a(1) =0a(2) =32a(3) =8051a(4) =290675a(5) =4353175a(6) =38761975a(7) =243824182a(8) =1194358326a(9) =4842169350a(10) =16924669350a(11) =52488756425a(12) =147511725257a(13) =381689190701a(14) =920589376525