Second column of the triangle A085843.

Terms

a(0) =1a(1) =4a(2) =16a(3) =67a(4) =294a(5) =1346a(6) =6397a(7) =31405a(8) =158531a(9) =819438a(10) =4321316a(11) =23176629a(12) =126086986a(13) =694259790a(14) =3862070512a(15) =21673114457a(16) =122545849017a(17) =697461040394