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

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =1a(5) =4a(6) =3a(7) =14a(8) =13a(9) =49a(10) =46a(11) =186a(12) =181a(13) =714a(14) =700a(15) =2789a(16) =2780a(17) =11050a(18) =10997a(19) =43946a(20) =43895a(21) =175259a(22) =175088a(23) =700074a(24) =699875a(25) =2798246a(26) =2797536a(27) =11188856a(28) =11188191a(29) =44747434