a(0)=1; for n>0, p2(n)+Sum(binomial(2*k,k)*p2(n-k)/2,k=1..n-1) where p2 = A002995, the number of unlabeled planar trees on n nodes.
A191280
a(0)=1; for n>0, p2(n)+Sum(binomial(2*k,k)*p2(n-k)/2,k=1..n-1) where p2 = A002995, the number of unlabeled planar trees on n nodes.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =18a(5) =60a(6) =210a(7) =754a(8) =2766a(9) =10280a(10) =38568a(11) =145770a(12) =554162a(13) =2116568a(14) =8115660a(15) =31220672a(16) =120442860a(17) =465775226a(18) =1805074882a(19) =7008550224a(20) =27257398714a(21) =106166467074a(22) =414068416752
External references
- oeis: A191280