A137745 - OEIS

%I #18 Jun 11 2024 01:50:30

%S 0,0,0,0,0,1,5,19,66,218,700,2218,6997,22064,69662,220395,699090,

%T 2224114,7098773,22733498,73048903,235504760,761689193,2471105355

%N Number of different strings of length n obtained from "abcde" 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<5, since no shorter string can be obtained by duplicating a substring.

%e a(5) = # { abcde },

%e a(6) = # { aabcde, abbcde, abccde, abcdde, abcdee },

%e a(7) = # { aaabcde, aabbcde, aabccde, aabcdde, aabcdee, ababcde, abbbcde, abbccde, abbcdde, abbcdee, abcbcde, abcccde, abccdde, abccdee, abcdcde, abcddde, abcddee, abcdede, abcdeee }

%o (PARI) A135473(13,5) /* function defined in A137743...*/

%Y Cf. A137740-A137743, A135473, A137744-A137748.

%K more,nonn

%O 0,7

%A _M. F. Hasler_, Feb 10 2008

%E a(14)-a(19) from _Lars Blomberg_, Jan 12 2013

%E a(20)-a(21) from _Michael S. Branicky_, Jan 05 2021

%E a(22)-a(23) from _Bert Dobbelaere_, Jun 10 2024