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 A137746 Number of different strings of length n obtained from "abcdef" by iteratively duplicating any substring. 4
 0, 0, 0, 0, 0, 0, 1, 6, 26, 100, 360, 1246, 4217, 14102, 46861, 155212, 513336, 1697264, 5614670, 18594258 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,8 COMMENTS See A137743 for more comments. LINKS EXAMPLE a(k) = 0 for k<6, since no shorter string can be obtained by duplication a(6) = 1 = # { abcdef }, a(7) = 6 = # { aabcdef, abbcdef, abccdef, abcddef, abcdeef, abcdeff }, 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 }. PROG (PARI) A135473(14, 6) /* function defined in A137743 ... */ CROSSREFS Cf. A137740, A137741, A137742, A137743, A135473, A137744, A137745, A137746, A137747, A137748. Sequence in context: A186314 A234267 A055420 * A261064 A094811 A005022 Adjacent sequences:  A137743 A137744 A137745 * A137747 A137748 A137749 KEYWORD more,nonn AUTHOR M. F. Hasler, Feb 10 2008 EXTENSIONS a(15)-a(16) from Alois P. Heinz, Aug 31 2011 a(17)-a(19) from Lars Blomberg, Jan 12 2013 STATUS approved

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Last modified June 1 13:11 EDT 2020. Contains 334762 sequences. (Running on oeis4.)