Number of B-trees of order 4 with n leaves.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =4a(7) =5a(8) =9a(9) =15a(10) =28a(11) =45a(12) =73a(13) =116a(14) =199a(15) =345a(16) =601a(17) =1021a(18) =1738a(19) =2987a(20) =5244a(21) =9321a(22) =16720a(23) =30103a(24) =54345a(25) =97996a(26) =176011a(27) =314045a(28) =556577a(29) =980852