Number of periodic palindromic structures of length n using exactly five different symbols.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =1a(9) =10a(10) =15a(11) =85a(12) =140a(13) =618a(14) =1050a(15) =4065a(16) =6951a(17) =24915a(18) =42525a(19) =145067a(20) =246730a(21) =814215a(22) =1379400a(23) =4446631a(24) =7508501a(25) =23798600a(26) =40075035a(27) =125436313a(28) =210766920a(29) =653517228