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A280149 Numbers k such that 3^k - 2^k is not squarefree. 7
10, 11, 20, 22, 30, 33, 40, 42, 44, 50, 52, 55, 57, 60, 66, 70, 77, 80, 84, 88, 90, 99, 100, 104, 110, 114, 120, 121, 126, 130, 132, 140, 143, 150, 154, 156, 160, 165, 168, 170, 171, 176, 180, 187, 190, 198, 200, 203, 208, 209, 210, 220, 228, 230, 231, 240, 242, 250, 252, 253, 260, 264, 270, 272, 275, 280, 285 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Primitive members (not multiples of earlier terms) are 10, 11, 42, 52, 57, 203, 272, 497, .... - Juri-Stepan Gerasimov and Charles R Greathouse IV, Dec 27 2016
From Robert Israel, Dec 27 2016: (Start)
Numbers divisible by the order of 3/2 mod p^2 for some prime p > 3.
Includes numbers divisible by p^2-p for some prime p > 3.
If k is a member, then so are all multiples of k. (End)
LINKS
Charles R Greathouse IV and Amiram Eldar, Table of n, a(n) for n = 1..134 (terms 1..127 from Charles R Greathouse IV)
EXAMPLE
10 is in this sequence because 3^10 - 2^10 = 58025 = 5^2*11*211.
MATHEMATICA
Select[Range@ 120, ! SquareFreeQ[3^# - 2^#] &] (* Michael De Vlieger, Dec 27 2016 *)
PROG
(Magma) [n: n in [1..156] | not IsSquarefree(3^n-2^n)];
(PARI) is(n)=issquarefree(3^n-2^n)==0 \\ Charles R Greathouse IV, Dec 27 2016
CROSSREFS
Sequence in context: A007623 A109827 A109839 * A087486 A284375 A102626
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Charles R Greathouse IV, Dec 27 2016
STATUS
approved

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Last modified June 22 22:30 EDT 2024. Contains 373622 sequences. (Running on oeis4.)