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A107036 Indices of prime Jacobsthal numbers. 13

%I

%S 3,4,5,7,11,13,17,19,23,31,43,61,79,101,127,167,191,199,313,347,701,

%T 1709,2617,3539,5807,10501,10691,11279,12391,14479,42737,83339,95369,

%U 117239,127031,138937,141079,267017,269987,374321

%N Indices of prime Jacobsthal numbers.

%C All a(n) are prime except a(1) = 4. All prime a(n) are listed in A000978[n] = {3,5,7,11,13,17,19,23,31,43,61,79,101,127,167,...} Numbers n such that (2^n + 1)/3 is prime. - _Alexander Adamchuk_, Oct 03 2006

%F a(n) = A000978(n) for n>1. - _Alexander Adamchuk_, Oct 03 2006

%o (PARI) is(n)=ispseudoprime((2^n - (-1)^n) / 3) \\ _Charles R Greathouse IV_, Apr 28 2015

%Y Cf. A000978, A001045, A001605.

%K nonn

%O 0,1

%A _Paul Barry_, May 09 2005

%E More terms from _Alexander Adamchuk_, Oct 03 2006

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Last modified March 22 04:32 EDT 2019. Contains 321406 sequences. (Running on oeis4.)