a(n) = Sum_{k=1..n-1} binomial(n, k)*2^(n-k-1)*(k-1).

Terms

a(0) =0a(1) =0a(2) =3a(3) =20a(4) =95a(5) =394a(6) =1519a(7) =5592a(8) =19935a(9) =69398a(10) =237215a(11) =799204a(12) =2661295a(13) =8776962a(14) =28714191a(15) =93300656a(16) =301392575a(17) =968682286a(18) =3099626047a(19) =9879746748a(20) =31382108175a(21) =99375452570a(22) =313814790383a(23) =988511766280