Column 1 of triangle A091615.

Terms

a(0) =1a(1) =2a(2) =6a(3) =11a(4) =26a(5) =61a(6) =132a(7) =290a(8) =638a(9) =1390a(10) =3012a(11) =6496a(12) =13940a(13) =29793a(14) =63450a(15) =134628a(16) =284764a(17) =600596a(18) =1263304a(19) =2650684a(20) =5549117a(21) =11592553a(22) =24170837a(23) =50306424a(24) =104527509a(25) =216852455a(26) =449232326a(27) =929378744a(28) =1920295902a(29) =3963077103