Number of 4-divided binary words of length n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =11a(7) =37a(8) =109a(9) =287a(10) =698a(11) =1617a(12) =3642a(13) =7985a(14) =17208a(15) =36620a(16) =77093a(17) =161027a(18) =334205a(19) =690080a(20) =1418917a(21) =2907655a(22) =5941148a(23) =12110674