A000904(n) - (-1)^n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =14a(4) =82a(5) =593a(6) =4820a(7) =43980a(8) =444612a(9) =4934721a(10) =59661254a(11) =780531034a(12) =10987095718a(13) =165586966817