Smooth necklaces with 4 colors.

Terms

a(0) =1a(1) =4a(2) =7a(3) =12a(4) =25a(5) =51a(6) =121a(7) =272a(8) =656a(9) =1563a(10) =3794a(11) =9193a(12) =22529a(13) =55189a(14) =136025a(15) =335942a(16) =832605a(17) =2068070a(18) =5150558a(19) =12852754a(20) =32139908a(21) =80509629a(22) =202016993a(23) =507669052a(24) =1277595853a(25) =3219366640a(26) =8122296152