Number of paths in B(n) that start with a u step and end with a d step.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =1a(5) =2a(6) =5a(7) =11a(8) =26a(9) =62a(10) =148a(11) =356a(12) =860a(13) =2085a(14) =5073a(15) =12382a(16) =30309a(17) =74391a(18) =183042a(19) =451427a(20) =1115741a(21) =2763228a(22) =6856327a(23) =17042633a(24) =42433166a(25) =105816857a(26) =264268595a(27) =660908408a(28) =1655040445a(29) =4149700172