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A020339 p^2 is least square base n doublet (base n representation is the concatenation of 2 identical strings). 8
6, 2, 615, 84, 119973, 4, 3, 23620, 36363636364, 6, 24766945690, 17928148, 915, 4, 86808207405692007605, 6, 130, 10, 2667, 95530227420606, 10623969116570, 12, 5, 343872950627253606, 9, 14, 59239353339085, 8130 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

The identical strings must contain at least one nonzero digit, so that a(n) > 0. - Alonso del Arte, Jun 20 2018

REFERENCES

David Wells, "The Penguin Dictionary of Curious and Interesting Numbers", Revised Edition 1997, p. 189.

LINKS

Table of n, a(n) for n=2..29.

A. Ottens, The arithmetic-digits-squares-three.digits problem [Broken link?]

EXAMPLE

The first few squares in binary are: 1, 100, 1001, 10000, 11001, 100100. Thus we see that 100100, which is 36 in decimal, the square of 6, is the first square which is the concatenation of two identical bit patterns, and therefore a(2) = 6.

CROSSREFS

Cf. A020340, A054214, A054215, A054216, A030465, A030466, A030467.

Sequence in context: A100251 A266607 A290051 * A154738 A195738 A184082

Adjacent sequences:  A020336 A020337 A020338 * A020340 A020341 A020342

KEYWORD

base,nonn

AUTHOR

David W. Wilson

EXTENSIONS

Name slightly adjusted by Alonso del Arte, Jun 20 2018

STATUS

approved

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Last modified December 18 21:01 EST 2018. Contains 318245 sequences. (Running on oeis4.)