OK, I may have the correct conjecture now. Let C2=0.660161815846869573927812110014... be the Hardy Littlewood twin prime constant described here http://en.wikipedia.org/wiki/Twin_prime#First_Hardy.E2.80.93Littlewood_conje... Then let B = exp(-2*C2 / ln2) = 0.14884878474999065378100135978. Then my conjecture is, that the proportion of primes which are "every bit matters" primes, (i.e. if you alter any bit in their binary expansion, you get a composite; here we do not regard leading 0s as "bits") is B. Not hugely convincingly, I computed that among the 50847534 primes below 10^9, 7179982, which is 14.121%, are every-bit-matters primes. Perhaps going to 10^12 or something would be more convincing. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)