Number of primitive (period n) periodic palindromes using exactly five different symbols.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =60a(8) =120a(9) =960a(10) =1800a(11) =9300a(12) =16800a(13) =71400a(14) =126000a(15) =480000a(16) =834120a(17) =2968440a(18) =5103000a(19) =17354340a(20) =29607600a(21) =97566000a(22) =165528000a(23) =533264700a(24) =901020120a(25) =2854995360a(26) =4809004080a(27) =15050445900a(28) =25292030400a(29) =78417321240