

A320434


Number of lengthn quasiperiodic binary strings.


2



0, 2, 2, 4, 4, 10, 10, 26, 22, 56, 68, 118, 126, 284, 274, 542, 604, 1144, 1196, 2284, 2340, 4600, 4876, 9010, 9280, 18286, 18476, 35546, 36886, 70320, 72092, 140578, 141736, 276812, 282694
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OFFSET

1,2


COMMENTS

A lengthn string x is quasiperiodic if some proper prefix t of x can completely cover x by shifting, allowing overlaps. For example, 01010010 is quasiperiodic because it can be covered by shifted occurrences of 010.


LINKS

Table of n, a(n) for n=1..35.
A. Apostolico, M. Farach, and C. S. Iliopoulos, Optimal superprimitivity testing for strings, Info. Proc. Letters 39 (1991), 1720.
Rémy Sigrist, C program for A320434


FORMULA

a(n) = 2^n  A216215(n).  Rémy Sigrist, Jan 08 2019


EXAMPLE

For n = 5 the quasiperiodic strings are 00000, 01010, and their complements.


PROG

(C) See Links section.


CROSSREFS

Cf. A216215.
Sequence in context: A286088 A005293 A287488 * A329394 A057784 A209284
Adjacent sequences: A320431 A320432 A320433 * A320435 A320436 A320437


KEYWORD

nonn,more


AUTHOR

Jeffrey Shallit, Jan 08 2019


EXTENSIONS

a(18)a(30) from Rémy Sigrist, Jan 08 2019
a(31)a(35) from Rémy Sigrist, Jan 09 2019


STATUS

approved



