a(n) = Sum_{i=1..n} n^i * (n - i).

Terms

a(0) =0a(1) =2a(2) =15a(3) =108a(4) =970a(5) =11190a(6) =160125a(7) =2739128a(8) =54480996a(9) =1234567890a(10) =31384283755a(11) =884241366756