Number of 4-ary Lyndon words of length n with exactly three 1s.

Terms

a(0) =3a(1) =18a(2) =89a(3) =405a(4) =1701a(5) =6801a(6) =26244a(7) =98415a(8) =360846a(9) =1299078a(10) =4605822a(11) =16120350a(12) =55801305a(13) =191318760a(14) =650483703a(15) =2195382771a(16) =7360989291a(17) =24536630727a(18) =81358302690a(19) =268482398877a(20) =882156452724