Number of primitive (aperiodic) palindromes using a maximum of four different symbols.

Terms

a(0) =4a(1) =0a(2) =12a(3) =12a(4) =60a(5) =48a(6) =252a(7) =240a(8) =1008a(9) =960a(10) =4092a(11) =4020a(12) =16380a(13) =16128a(14) =65460a(15) =65280a(16) =262140a(17) =261072a(18) =1048572a(19) =1047540a(20) =4194036a(21) =4190208a(22) =16777212a(23) =16772880a(24) =67108800a(25) =67092480a(26) =268434432a(27) =268419060a(28) =1073741820a(29) =1073675280