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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

Table of n, a(n) for n=0..19.

Index entries for doubling substrings

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 November 19 14:52 EST 2018. Contains 317352 sequences. (Running on oeis4.)