%I #11 Feb 18 2019 06:21:20
%S 1,2,3,5,6,7,10,13,14,15,17,19,26,30,31,34,38,43,51,61,62,65,79,85,86,
%T 89,93,95,107,122,127,129,130,133,158,170,193,254,255,301,311,331,349,
%U 389,445,521,557,577,579,607,631,647,1103,1167
%N Positive integers k such that each prime divisor of 2^k - 1 has the form 4j + 3.
%C The exponents of the Mersenne primes (A000043) are contained in this sequence.
%C Needed factorizations are in the Cunningham Project.
%H S. S. Wagstaff, Jr., <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>.
%F A183075(n) = 2^a(n) - 1.
%e 6 is in this sequence because 2^6 - 1 = 3^2 * 7, and 3 and 7 have the form 4j + 3.
%Y Cf. A000043, A136003, A183072, A183073, A183074.
%Y Cf. A000668, A136005, A183075, A183076, A183077, A183078.
%K nonn
%O 1,2
%A _Stuart Clary_, Dec 23 2010
%E a(53)-a(54) from _Amiram Eldar_, Feb 18 2019