A137746 - OEIS

%I #29 Jun 11 2024 12:05:52

%S 0,0,0,0,0,0,1,6,26,100,360,1246,4217,14102,46861,155212,513336,

%T 1697264,5614670,18594258,61671770,204907302,682110940,2275141754

%N Number of different strings of length n obtained from "abcdef" by iteratively duplicating any substring.

%C See A137743 for more comments.

%H <a href="/index/Do#repeat">Index entries for doubling substrings</a>

%e a(k) = 0 for k<6, since no shorter string can be obtained by duplication

%e a(6) = 1 = # { abcdef },

%e a(7) = 6 = # { aabcdef, abbcdef, abccdef, abcddef, abcdeef, abcdeff },

%e a(8) = 26 = # { aaabcdef, aabbcdef, aabccdef, aabcddef, aabcdeef, aabcdeff, ababcdef, abbbcdef, abbccdef, abbcddef, abbcdeef, abbcdeff, abcbcdef, abcccdef, abccddef, abccdeef, abccdeff, abcdcdef, abcdddef, abcddeef, abcddeff, abcdedef, abcdeeef, abcdeeff, abcdefef, abcdefff }.

%o (PARI) A135473(14,6) /* function defined in A137743 ... */

%Y Cf. A137740, A137741, A137742, A137743, A135473, A137744, A137745, A137746, A137747, A137748.

%K more,nonn

%O 0,8

%A _M. F. Hasler_, Feb 10 2008

%E a(15)-a(16) from _Alois P. Heinz_, Aug 31 2011

%E a(17)-a(19) from _Lars Blomberg_, Jan 12 2013

%E a(20)-a(21) from _Michael S. Branicky_, Jan 06 2021

%E a(22)-a(23) from _Bert Dobbelaere_, Jun 11 2024