Number of meanders of length n.

Terms

a(0) =1a(1) =3a(2) =5a(3) =12a(4) =17a(5) =47a(6) =65a(7) =169a(8) =279a(9) =645a(10) =1025a(11) =2698a(12) =4097a(13) =9917a(14) =17345a(15) =39698a(16) =65537a(17) =161395a(18) =262145a(19) =624004a(20) =1089007a(21) =2449881a(22) =4194305a(23) =10097733a(24) =16812683a(25) =38754747a(26) =69117097a(27) =155178266a(28) =268435457a(29) =629929761