Number of Lyndon words on {1, 2, 3} with an even number of 1's.

Terms

a(0) =2a(1) =1a(2) =4a(3) =8a(4) =24a(5) =56a(6) =156a(7) =400a(8) =1092a(9) =2928a(10) =8052a(11) =22080a(12) =61320a(13) =170664a(14) =478288a(15) =1344800a(16) =3798240a(17) =10760568a(18) =30585828a(19) =87166656a(20) =249055976a(21) =713197848a(22) =2046590844a(23) =5883926400a(24) =16945772184a(25) =48881973840a(26) =141214767876a(27) =408513980160