Number of primitive (aperiodic) palindromic structures using exactly three different symbols.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =6a(7) =6a(8) =25a(9) =24a(10) =90a(11) =89a(12) =301a(13) =295a(14) =965a(15) =960a(16) =3025a(17) =2999a(18) =9330a(19) =9305a(20) =28495a(21) =28411a(22) =86526a(23) =86430a(24) =261624a(25) =261324a(26) =788945a(27) =788669a(28) =2375101a(29) =2374110