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A272475 Numbers n such that 2^n-1 and 3^n-1 are not coprime. 1

%I

%S 4,6,8,10,11,12,16,18,20,22,23,24,28,30,32,33,35,36,40,42,43,44,46,48,

%T 50,52,54,55,56,58,60,64,66,68,69,70,72,75,76,77,78,80,82,83,84,86,88,

%U 90,92,95,96,99,100,102,104,105,106,108,110,112,114,115,116,117

%N Numbers n such that 2^n-1 and 3^n-1 are not coprime.

%C Complement of A263647.

%H Vincenzo Librandi, <a href="/A272475/b272475.txt">Table of n, a(n) for n = 1..1000</a>

%e gcd(2^4-1, 3^4-1) = gcd(15,80) = 5, so a(1) = 4.

%t Select[Range[200], ! GCD[2^# - 1, 3^# - 1] == 1 &]

%o (MAGMA) [n: n in [1..200] | not Gcd(2^n-1, 3^n-1) eq 1];

%o (PARI) isok(n) = gcd(2^n-1, 3^n-1) != 1; \\ _Michel Marcus_, May 01 2016

%Y Cf. A263647.

%K nonn

%O 1,1

%A _Vincenzo Librandi_, May 01 2016

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Last modified October 14 05:08 EDT 2019. Contains 327995 sequences. (Running on oeis4.)