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A262068 Number of binary strings of length 2n that can be written as the concatenation of one or more squares. 1
1, 2, 6, 22, 76, 268, 926, 3250, 11328, 39658, 138534, 484364, 1693078, 5918780, 20690230, 72328158, 252841374, 883869956, 3089791576, 10801141656 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

By a "square" we mean a word of the form xx, where x is a string, like the English word "murmur".

a(0)=1 is by convention. - N. J. A. Sloane, Sep 17 2015

LINKS

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

EXAMPLE

For n = 2 the six words are 0000, 0011, 0101, and their complements.

MAPLE

for n from 1 to 13 do

B[n]:= convert(map(t-> t||t, StringTools:-Generate(n, "01")), set);

od:

C[0]:= {""}:

for n from 1 to 13 do

  C[n]:= {seq(seq(seq(cat(s, t), s=B[i]), t = C[n-i]), i=1..n)};

od:

seq(nops(C[n]), n=0..13); # Robert Israel, Sep 17 2015

CROSSREFS

Cf. A262278.

Sequence in context: A109194 A014334 A107239 * A148496 A217528 A181367

Adjacent sequences:  A262065 A262066 A262067 * A262069 A262070 A262071

KEYWORD

nonn,more

AUTHOR

Jeffrey Shallit, Sep 17 2015

EXTENSIONS

a(14)-a(19) from Lars Blomberg, Feb 03 2019

STATUS

approved

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Last modified April 20 02:06 EDT 2019. Contains 322291 sequences. (Running on oeis4.)