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A137744 Number of different strings of length n obtained from "abcd" by iteratively duplicating any substring. 11
0, 0, 0, 0, 1, 4, 13, 40, 119, 348, 1014, 2966, 8726, 25820, 76823, 229814, 691186, 2089850, 6351448, 19398726 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

See A137743 for more comments.

LINKS

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

Index entries for doubling substrings

EXAMPLE

a(4) = # { abcd },

a(5) = # { aabcd, abbcd, abccd, abcdd },

a(6) = # { aaabcd, aabbcd, aabccd, aabcdd, ababcd, abbbcd, abbccd, abbcdd, abcbcd, abcccd, abccdd, abcdcd, abcddd }

PROG

(PARI) A135473(12, 4)

CROSSREFS

Cf. A137740-A137743, A135473, A137745-A137748.

Sequence in context: A272581 A191132 A119915 * A027130 A027121 A238846

Adjacent sequences:  A137741 A137742 A137743 * A137745 A137746 A137747

KEYWORD

more,nonn

AUTHOR

M. F. Hasler, Feb 10 2008

EXTENSIONS

a(13)-a(19) from Lars Blomberg, Jan 12 2013

STATUS

approved

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Last modified October 17 09:42 EDT 2018. Contains 316276 sequences. (Running on oeis4.)