a(n) = (-1)^n * n * a(n-1) - 1, with a(0)=0.

Terms

a(0) =0a(1) =-1a(2) =-3a(3) =8a(4) =31a(5) =-156a(6) =-937a(7) =6558a(8) =52463a(9) =-472168a(10) =-4721681a(11) =51938490a(12) =623261879a(13) =-8102404428a(14) =-113433661993