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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. 2

%I #18 May 23 2024 04:28:28

%S 7,23,47,167,263,359,383,479,503,719,839,863,887,983,1319,1367,1439,

%T 1487,1823,2039,2063,2207,2447,2879,2903,2999,3023,3119,3167,3623,

%U 3863,4007,4079,4127,4679,4703,4799,4919,5087,5399,5639,5807,5879,5927,6047

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

%H Harvey P. Dale, <a href="/A101789/b101789.txt">Table of n, a(n) for n = 1..10000</a>

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

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

%o (PARI) is(k) = (k % 8 == 7) && isprime(k) && isprime(k\2); \\ _Amiram Eldar_, May 23 2024

%Y Intersection of A005385 and A007522.

%Y Cf. A002515.

%K easy,nonn

%O 1,1

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

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Last modified June 18 04:26 EDT 2024. Contains 373468 sequences. (Running on oeis4.)