First column (also row sums) of triangle in A099961.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =5a(7) =13a(8) =28a(9) =64a(10) =207a(11) =578a(12) =1685a(13) =6518a(14) =22361a(15) =79319a(16) =357180a(17) =1453177a(18) =6075215a(19) =31216968a(20) =146906126a(21) =707344776a(22) =4084254624a(23) =21823224623a(24) =118932148555a(25) =762346849634