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

Terms

a(0) =0a(1) =0a(2) =1a(3) =16a(4) =241a(5) =3936a(6) =71569a(7) =1452032a(8) =32724801a(9) =814205440a(10) =22221533401a(11) =661258764288