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A055859 a(n) and floor(a(n)/7) are both squares; i.e., squares which remain squares when written in base 7 and last digit is removed. 15
0, 1, 4, 9, 64, 256, 2025, 16129, 64516, 514089, 4096576, 16386304, 130576329, 1040514049, 4162056196, 33165873225, 264286471744, 1057145886976, 8424001222569, 67127723308801, 268510893235204, 2139663144659049, 17050177433963584, 68200709735854336 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Square roots of a(n) are listed in A204516, square roots of floor(a(n)/7) in A204517. - M. F. Hasler, Jan 16 2012

LINKS

Table of n, a(n) for n=1..24.

M. F. Hasler, Truncated squares, OEIS wiki, Jan 16 2012

Index to sequences related to truncating digits of squares.

FORMULA

a(n) = A204516(n)^2. - M. F. Hasler, Jan 16 2012

Empirical g.f.: -x^2*(9*x^8+256*x^7+64*x^6-270*x^5-764*x^4-191*x^3+9*x^2+4*x+1) / ((x-1)*(x^2+x+1)*(x^6-254*x^3+1)). - Colin Barker, Sep 15 2014

EXAMPLE

a(5) = 256 because 256 = 16^2 = 514 base 7 and 51 base 7 = 36 = 6^2.

CROSSREFS

Cf. A023110.

Sequence in context: A095175 A092396 A184877 * A162991 A062926 A069020

Adjacent sequences:  A055856 A055857 A055858 * A055860 A055861 A055862

KEYWORD

base,nonn

AUTHOR

Henry Bottomley, Jul 14 2000

STATUS

approved

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Last modified January 18 16:40 EST 2019. Contains 319271 sequences. (Running on oeis4.)