a(n) is the number of palindromic structures using a maximum of ten different symbols.

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) =678569a(22) =678569a(23) =4213530a(24) =4213530a(25) =27641927a(26) =27641927a(27) =190829797a(28) =190829797a(29) =1381367941