A072192 Indices of Sophie Germain primes: p and 2p+1 are primes.

1, 2, 3, 5, 9, 10, 13, 16, 23, 24, 30, 32, 40, 41, 43, 51, 52, 54, 60, 62, 72, 81, 83, 86, 94, 97, 108, 116, 119, 120, 124, 128, 132, 135, 140, 156, 162, 170, 171, 173, 176, 185, 200, 201, 209, 223, 228, 230, 234, 239, 240, 246

Offset: 1

Author

Miklos Kristof, Jul 02 2002

Keywords

• easy
• nonn

Examples

			5 is element of the sequence, P(5)=11 and 2*11+1=23 is prime.
		

References

• M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 870.
• J. Roberts, Lure of the Integers, Math. Assoc. America, 1992, p. 83.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].

Crossrefs

Cf. A005384, A000720.

Programs

Mathematica

Select[Range[250],PrimeQ[2Prime[#]+1]&] (* Harvey P. Dale, Feb 22 2017 *)

Formula

a(n) = A000720(A005384(n)). - Ridouane Oudra, Mar 07 2023