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%I #32 Jul 23 2017 22:15:21
%S 0,2,1,1,1,4,1,1,6,1,1,24,1,2,2,1,1,2,2,1,4,1,1,2,1,8,4,1,12,4,1,1,8,
%T 3,1,2,1,1,2,38,1,4,1,4,2,1,2,4,747,1,4,1,1,2,1,1,10,1,2,2,2,6,42,2,1,
%U 2,1,2,10,1,1,4,2,16,50,1,1,2,22,1,2,38
%N Least number k > 0 such that (2*n-1)^k - 2 is prime, or 0 if no such number exists.
%H Michel Marcus, <a href="/A255707/b255707.txt">Table of n, a(n) for n = 1..152</a> (terms 1..143 from Robert Price)
%H Carlos Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_887.htm">Puzzle 887. p(n)^c-2 is prime</a>, The Prime Puzzles and Problems Connection.
%F a(A098090(n)) = 1. - _Michel Marcus_, Mar 03 2015
%t lst = {0}; For[n = 2, n ≤ 143, n++, For[k = 1, k >= 1, k++, If[PrimeQ[(2*n - 1)^k - 2], AppendTo[lst, k]; Break[]]]]; lst
%o (PARI) a(n)=if(n==1,return(0));k=1;while(k,if(ispseudoprime((2*n-1)^k-2),return(k));k++)
%o vector(50,n,a(n)) \\ _Derek Orr_, Mar 03 2015
%Y Cf. A079706, A084712, A084713, A084714, A098090, A138066.
%K nonn
%O 1,2
%A _Robert Price_, Mar 02 2015
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