A307121 -id:A307121 - cp's OEIS frontend

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A307176 Number of Sophie Germain primes of the form 4k + 1 less than 10^n.

Original entry on oeis.org

1, 5, 17, 89, 589, 3833, 27940, 211439, 1653257, 13283194, 109058142, 911411528, 7731354496

Offset: 1

Rodolfo Ruiz-Huidobro, Mar 27 2019

Sophie Germain primes can alternatively be Lucasian primes, primes of the form 4k + 1, or, the individual prime 2.

			There are five Sophie Germain Primes of the form 4k + 1 below 10^2: {5, 29, 41, 53, 89}, therefore a(2) = 5.

Cf. A091098, A092816, A002515, A307121, A002144, A005384, A103579.

nonLucSophies = Select[4Range[2500000] + 1, PrimeQ[#] && PrimeQ[2# + 1] &]; Table[Length[Select[nonLucSophies, # < 10^n &]], {n, 0, 7}]

a(n) < A092816(n).
a(n) <= A091098(n) (with equality for n = 1).
a(n) = A092816(n) - A307121(n) - 1.

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