a(n) = number of strings of length n that can be obtained by starting with abc and repeatedly doubling any substring in place.

A135473

a(n) = number of strings of length n that can be obtained by starting with abc and repeatedly doubling any substring in place.

Terms

    a(0) =0a(1) =0a(2) =1a(3) =3a(4) =8a(5) =21a(6) =54a(7) =138a(8) =355a(9) =924a(10) =2432a(11) =6461a(12) =17301a(13) =46657a(14) =126656a(15) =345972a(16) =950611a(17) =2626253a(18) =7292268a(19) =20342805a(20) =56993909a(21) =160317859a(22) =452642235a(23) =1282466920a(24) =3645564511a(25) =10395117584a(26) =29727982740a(27) =85251828792a(28) =245120276345a(29) =706529708510

External references