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%I #32 Jun 06 2019 15:32:29
%S 1,5,17,89,589,3833,27940,211439,1653257,13283194,109058142,911411528,
%T 7731354496
%N Number of Sophie Germain primes of the form 4k + 1 less than 10^n.
%C Sophie Germain primes can alternatively be Lucasian primes, primes of the form 4k + 1, or, the individual prime 2.
%F a(n) < A092816(n).
%F a(n) <= A091098(n) (with equality for n = 1).
%F a(n) = A092816(n) - A307121(n) - 1.
%e There are five Sophie Germain Primes of the form 4k + 1 below 10^2: {5, 29, 41, 53, 89}, therefore a(2) = 5.
%t nonLucSophies = Select[4Range[2500000] + 1, PrimeQ[#] && PrimeQ[2# + 1] &]; Table[Length[Select[nonLucSophies, # < 10^n &]], {n, 0, 7}]
%Y Cf. A091098, A092816, A002515, A307121, A002144, A005384, A103579.
%K nonn,more
%O 1,2
%A _Rodolfo Ruiz-Huidobro_, Mar 27 2019