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 A137748 Number of different strings of length n obtained from "abcdefgh" by iteratively duplicating any substring. 11
 0, 0, 0, 0, 0, 0, 0, 0, 1, 8, 43, 196, 814, 3188, 12018, 44178, 159660, 570262, 2019964, 7112774, 24940259, 87191430, 304203350 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,10 COMMENTS See A137743 for more comments. LINKS EXAMPLE a(k) = 0 for k<8, since no shorter string can be obtained by duplication of substrings. a(8) = 1 = # { abcdefgh }, a(9) = 8 = # { aabcdefgh, abbcdefgh, abccdefgh, abcddefgh, abcdeefgh, abcdeffgh, abcdefggh, abcdefghh }, a(10) = (8+1)*(8+2)/2-2 = 43: for each letter we have one string of the form aaabcdefgh; for each 2-element subset {a,b}, {a,c},... we have the string with each of these two letters duplicated (i.e. aabbcdefgh, aabccdefgh,...), and for each of ab,bc,cd,...,gh we have the string with this substring duplicated (ababcdefgh,...,abcdefghgh). PROG (PARI) A135473(14, 8) /*function defined in A137743*/ CROSSREFS Cf. A137740-A137743, A135473, A137744-A137747. Sequence in context: A036647 A000429 A055853 * A005024 A094865 A122880 Adjacent sequences:  A137745 A137746 A137747 * A137749 A137750 A137751 KEYWORD more,nonn AUTHOR M. F. Hasler, Feb 10 2008 EXTENSIONS a(15)-a(17) from Alois P. Heinz, Sep 01 2011 a(18)-a(20) from Lars Blomberg, Jan 12 2013 a(21)-a(22) from Bert Dobbelaere, Dec 30 2018 STATUS approved

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Last modified June 25 06:59 EDT 2021. Contains 345452 sequences. (Running on oeis4.)