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%I #14 Nov 15 2013 10:59:04
%S 2,0,2,1,1,2,3,1,2,1,1,4,3,1,4,1,2,2,1,3,2,7,1,4,1,1,2,1,1,12,3,2,4,5,
%T 1,2,7,1,2,1,3,2,5,1,4,1,3,2,1,1,10,3,2,10,9,2,8,1,1,12,1,2,2,25,1,2,
%U 3,1,2,1,1,2,5,1,4,5,3,2,1,1,2,3,2,4,1,2,2,1,1,8,3,4,2,1,3,226,3,1,2
%N Smallest m >= 0 such that (2n-1)2^m-1 is prime, or -1 if no such value exists.
%C There exist odd integers 2k-1 such that (2k-1)2^n-1 is always composite.
%D Ribenboim, P., The New Book of Prime Number Records. New York: Springer-Verlag, pp. 357-359, 1996.
%H T. D. Noe, <a href="/A046069/b046069.txt">Table of n, a(n) for n=1..1000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/RieselNumber.html">Riesel Number.</a>
%t max = 10^6; (* this maximum value of m is sufficient up to n=1000 *) a[1] = 2; a[2] = 0; a[n_] := For[m = 1, m <= max, m++, If[PrimeQ[(2*n - 1)*2^m - 1], Return[m]]] /. Null -> -1; Reap[ Do[ Print[ "a(", n, ") = ", a[n]]; Sow[a[n]], {n, 1, 100}]][[2, 1]] (* _Jean-François Alcover_, Nov 15 2013 *)
%Y Cf. A046067, A046070.
%Y Bisection of A040081.
%K nonn
%O 1,1
%A _Eric W. Weisstein_
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