Number of palindromic structures of length n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =5a(6) =5a(7) =15a(8) =15a(9) =52a(10) =52a(11) =203a(12) =203a(13) =877a(14) =877a(15) =4140a(16) =4140a(17) =21147a(18) =21147a(19) =115975a(20) =115975a(21) =678570a(22) =678570a(23) =4213597a(24) =4213597a(25) =27644437a(26) =27644437a(27) =190899322a(28) =190899322a(29) =1382958545