OFFSET
1,1
COMMENTS
k is prime if and only if 2^(k - 1) is congruent to 1 mod k. The test relies on the Selfridge criterion (see p. 42 of the Krizek et al. reference).
REFERENCES
M. Krizek, F. Luca & L. Somer, 17 Lectures on Fermat Numbers, Springer-Verlag NY 2001, p. 42.
P. Ribenboim, The Little Book of Bigger Primes, Springer Science & Business Media, 2013, pp. 32-33.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
map(t->2*t+1, select(isprime, [2, seq(4*k+1, k=1..1000)])); # Robert Israel, Feb 27 2018
MATHEMATICA
Select[2*Prime@Range[109] + 1, ! Mod[#, 8] == 7 &]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Arkadiusz Wesolowski, Feb 09 2018
STATUS
approved