Number of primitive (period n) periodic palindromic structures using exactly four different symbols.

A056521

Number of primitive (period n) periodic palindromic structures using exactly four different symbols.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =7a(8) =10a(9) =43a(10) =65a(11) =219a(12) =350a(13) =1058a(14) =1701a(15) =4796a(16) =7770a(17) =21094a(18) =34105a(19) =90205a(20) =145749a(21) =379326a(22) =611501a(23) =1573205a(24) =2532530a(25) =6465123a(26) =10391735a(27) =26378849a(28) =42355950a(29) =107089814

External references