Number of left factors of peakless Motzkin paths of length n.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =21a(5) =50a(6) =121a(7) =296a(8) =730a(9) =1812a(10) =4521a(11) =11328a(12) =28485a(13) =71844a(14) =181674a(15) =460443a(16) =1169283a(17) =2974574a(18) =7578937a(19) =19337489a(20) =49401526a(21) =126350742a(22) =323495259a(23) =829033334a(24) =2126454271a(25) =5458711430a(26) =14023219126a(27) =36049991901a(28) =92734505565