%I A124977
%S A124977 0,4700063497,19147,25,2228071,262279,95,481,45,2873,3175999,555,95921,
%T A124977 174934013,777,140039,2463240427,477,91,623,2453,55,345119,1131,943,21967,
%U A124977 135,46979,125,3811,23329,155,1064959,245
%N A124977 Least positive number k such that 2^k (mod k) == 2n+1, or 0 if no such 
               k exists.
%e A124977 a(3) = 25 because 2^25 = 33554432 = 7 + 25*1342177.
%Y A124977 A bisection of A036236: a(n) = A036236(2n+1). Cf. A122182.
%Y A124977 Cf. A050259 = numbers n such that 2^n == 3 (mod n), A033981 = 2^n (mod 
               n) == 7, A124974 = 2^n (mod n) == 17, A124965 = Odd values of 2^n 
               (mod n) corresponding to the n's given in A015911, A015910 = 2^n 
               (mod n), A015911 = 2^n (mod n) is odd.
%Y A124977 Cf. A015910, A015911, A033981, A050259, A124965, A124974.
%Y A124977 Sequence in context: A114670 A092776 A034916 this_sequence A128172 A050259 
               A015384
%Y A124977 Adjacent sequences: A124974 A124975 A124976 this_sequence A124978 A124979 
               A124980
%K A124977 nonn
%O A124977 0,2
%A A124977 Zak Seidov (zakseidov(AT)yahoo.com), Nov 14 2006