Number of meanders of length n with Motzkin-steps avoiding the consecutive steps DD.

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =34a(5) =90a(6) =240a(7) =643a(8) =1729a(9) =4662a(10) =12597a(11) =34095a(12) =92406a(13) =250719a(14) =680877a(15) =1850457a(16) =5032296a(17) =13692674a(18) =37274438a(19) =101509476a(20) =276535824a(21) =753574253a(22) =2054064713a(23) =5600176231a(24) =15271331416a(25) =41651397245a(26) =113618996429a(27) =309979833301a(28) =845805408448