Number of 3-divided binary sequences (or words) of length n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =7a(5) =23a(6) =54a(7) =132a(8) =290a(9) =634a(10) =1342a(11) =2834a(12) =5868a(13) =12140a(14) =24899a(15) =50929a(16) =103735a(17) =210901a(18) =427623a(19) =865910a(20) =1750505a(21) =3535098a(22) =7131321a(23) =14374647a(24) =28952661a(25) =58280123a(26) =117248217a(27) =235770302a(28) =473897980a(29) =952183214