a(n) = Sum_{k=0..n} (k+1) * A026670(n, k).

Terms

a(0) =1a(1) =3a(2) =10a(3) =25a(4) =69a(5) =161a(6) =412a(7) =927a(8) =2275a(9) =5005a(10) =11958a(11) =25909a(12) =60753a(13) =130185a(14) =301064a(15) =639761a(16) =1463787a(17) =3090217a(18) =7010750a(19) =14722575a(20) =33171193a(21) =69357949a(22) =155376996a(23) =323702075a(24) =721673251a(25) =1498859829a(26) =3327877658a(27) =6893460863