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A319293 Numbers of the form 27^i*(9*j +- 1). 1

%I

%S 1,8,10,17,19,26,27,28,35,37,44,46,53,55,62,64,71,73,80,82,89,91,98,

%T 100,107,109,116,118,125,127,134,136,143,145,152,154,161,163,170,172,

%U 179,181,188,190,197,199,206,208,215,216,217,224,226,233,235,242,244

%N Numbers of the form 27^i*(9*j +- 1).

%C {+-a(n)} gives all nonzero cubes modulo all powers of 3, that is, cubes over 3-adic integers. So this sequence is closed under multiplication.

%H Jianing Song, <a href="/A319293/b319293.txt">Table of n, a(n) for n = 1..9231</a> (all terms <= 40000)

%F a(n) = 13*n/3 + O(log(n)).

%o (PARI) isA319293(n)= n\27^valuation(n, 27)%9==1||n\27^valuation(n, 27)%9==8

%Y A056020 is a proper subsequence.

%Y Perfect powers over 3-adic integers:

%Y Squares: positive: A055047; negative: A055048 (negated);

%Y Cubes: this sequence.

%K nonn

%O 1,2

%A _Jianing Song_, Sep 16 2018

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Last modified May 6 17:59 EDT 2021. Contains 343586 sequences. (Running on oeis4.)