Partial sums of A000149.

Terms

a(0) =1a(1) =3a(2) =10a(3) =30a(4) =84a(5) =232a(6) =635a(7) =1731a(8) =4711a(9) =12814a(10) =34840a(11) =94714a(12) =257468a(13) =699881a(14) =1902485a(15) =5171502a(16) =14057612a(17) =38212564a(18) =103872533a(19) =282354833a(20) =767520028a(21) =2086335762a(22) =5671248608a(23) =15416052054a(24) =41905174183a(25) =113910073520a(26) =309639682948