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

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =1a(5) =4a(6) =3a(7) =13a(8) =12a(9) =39a(10) =36a(11) =121a(12) =116a(13) =364a(14) =351a(15) =1088a(16) =1080a(17) =3280a(18) =3237a(19) =9841a(20) =9800a(21) =29510a(22) =29403a(23) =88573a(24) =88440a(25) =265716a(26) =265356a(27) =797121a(28) =796796a(29) =2391484