a(n) = n*a(n-1) - a(n-2) + 1 + (-1)^n.

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =31a(5) =147a(6) =853a(7) =5824a(8) =45741a(9) =405845a(10) =4012711a(11) =43733976a(12) =520795003a(13) =6726601063a(14) =93651619881