A101789 Safe primes of the form 8*k-1: primes of the form 8*k-1 such that 4*k-1 is also a prime.

7, 23, 47, 167, 263, 359, 383, 479, 503, 719, 839, 863, 887, 983, 1319, 1367, 1439, 1487, 1823, 2039, 2063, 2207, 2447, 2879, 2903, 2999, 3023, 3119, 3167, 3623, 3863, 4007, 4079, 4127, 4679, 4703, 4799, 4919, 5087, 5399, 5639, 5807, 5879, 5927, 6047

Offset: 1

Author

Douglas Stones (dssto1(AT)student.monash.edu.au), Dec 16 2004

Keywords

• easy
• nonn

Examples

			4*1-1 = 3 and 8*1-1 = 7 are primes, so the first term is 7.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Intersection of A005385 and A007522.

Cf. A002515.

Programs

Mathematica

Select[Prime[Range[800]],Mod[#,8]==7&&PrimeQ[(#-1)/2]&] (* Harvey P. Dale, Jan 31 2012 *)

PARI

is(k) = (k % 8 == 7) && isprime(k) && isprime(k\2); \\ Amiram Eldar, May 23 2024