Start with x, xy; then concatenate each word in turn with all preceding words, getting x xy xxy xxxy xyxxy xxxxy xyxxxy xxyxxxy ...; sequence gives number of words of length n. Also binary trees by degree: x (x,y) (x,(x,y)) (x,(x,(x,y))) ((x,y),(x,(x,y)))...
A063895
Start with x, xy; then concatenate each word in turn with all preceding words, getting x xy xxy xxxy xyxxy xxxxy xyxxxy xxyxxxy ...; sequence gives number of words of length n. Also binary trees by degree: x (x,y) (x,(x,y)) (x,(x,(x,y))) ((x,y),(x,(x,y)))...
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =6a(7) =11a(8) =22a(9) =43a(10) =88a(11) =179a(12) =372a(13) =774a(14) =1631a(15) =3448a(16) =7347a(17) =15713a(18) =33791a(19) =72923a(20) =158021a(21) =343495a(22) =749102a(23) =1638103a(24) =3591724a(25) =7893802a(26) =17387931a(27) =38379200a(28) =84875596a(29) =188036830
External references
- oeis: A063895