OFFSET
1,2
COMMENTS
Terms are all even for n > 3.
Sophie Germain primes > 3 such that the number of primes of the form 2p - x is equal to the number of primes of the form 2p + y where x, y are divisors of 2p.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
3 is in this sequence because 3 - 1 = 2 is prime and 3 - 3 = 0, but 3 + 1 = 4 and 3 + 3 = 6, where 1, 3 are divisors of 3 and 0, 4, 6 are nonprimes.
MATHEMATICA
p[n_]:=If[PrimeQ[n], 1, 0]; Select[Range@ 202, Sum[p[# - d], {d, Divisors[Factor[#]]}] != Sum[p[# + d], {d, Divisors[Factor[#]]}] &] (* Indranil Ghosh, Mar 15 2017 *)
PROG
(PARI) is(n)=my(f=factor(n)); sumdiv(f, d, isprime(n-d)) != sumdiv(f, d, isprime(n+d)) \\ Charles R Greathouse IV, Mar 15 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 15 2017
EXTENSIONS
Corrected by Charles R Greathouse IV, Mar 15 2017
STATUS
approved