a(n) = Sum_{j=0..12} (-n)^j.

Terms

a(0) =1a(1) =1a(2) =2731a(3) =398581a(4) =13421773a(5) =203450521a(6) =1865813431a(7) =12111126301a(8) =61083979321a(9) =254186582833a(10) =909090909091