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A177103 Numbers n >= 0 such that 2*3^n - 1 is not prime. 1

%I

%S 0,4,5,6,9,10,11,13,14,15,16,17,18,19,21,22,24,25,26,28,29,30,31,32,

%T 33,34,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,57,

%U 58,59,60,61,63,64,65,66,67,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84

%N Numbers n >= 0 such that 2*3^n - 1 is not prime.

%H Vincenzo Librandi, <a href="/A177103/b177103.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[0, 100], !PrimeQ[2*3^# - 1] &] (* _Vincenzo Librandi_, Oct 15 2012 *)

%o (MAGMA) [ n: n in [0..100] | not IsPrime(2*3^n-1) ];

%Y Cf. A003307 (Numbers n such that 2*3^n-1 is prime).

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_

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Last modified June 20 05:01 EDT 2019. Contains 324229 sequences. (Running on oeis4.)