Quote:
Originally Posted by T.Rex
Up to now, for c>0, they all seem to appear when c = 1 mod 8 : 1, 17, 25, 33, 41, 73 .

There are also pseudo primes for c=89, but not with 81, 87, 105, with the following bounds:
for(k=1,300,CEk2c(k,89,300)) :
133*2^262+89
221*2^291+89
266*2^261+89