a(n) = 2^(n-2) * (n! + floor(n/2)!).

Terms

a(0) =1a(1) =1a(2) =3a(3) =14a(4) =104a(5) =976a(6) =11616a(7) =161472a(8) =2582016a(9) =46451712a(10) =929003520a(11) =20437463040a(12) =490498375680