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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =6a(5) =6a(6) =36a(7) =36a(8) =150a(9) =144a(10) =540a(11) =534a(12) =1806a(13) =1770a(14) =5790a(15) =5760a(16) =18150a(17) =17994a(18) =55980a(19) =55830a(20) =170970a(21) =170466a(22) =519156a(23) =518580a(24) =1569744a(25) =1567944a(26) =4733670a(27) =4732014a(28) =14250606a(29) =14244660