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Primes p such that (p-7)/8 and 8p + 7 are both prime.
1

%I #7 Mar 24 2015 14:45:51

%S 23,47,863,1103,1439,1583,1823,2879,3359,4943,5279,6719,7823,8783,

%T 9743,11279,11903,12479,13103,16703,18719,19583,20399,20879,21503,

%U 23279,23663,25343,26399,27743,29759,33119,35279,38303,39359,39503,41183

%N Primes p such that (p-7)/8 and 8p + 7 are both prime.

%H Harvey P. Dale, <a href="/A158238/b158238.txt">Table of n, a(n) for n = 1..1000</a>

%F 23, (23-7)/8=2, and 8*23+7=191 are all prime.

%t Select[Prime[Range[5000]],AllTrue[{(#-7)/8,8#+7},PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Mar 24 2015 *)

%o (PARI) isok(p) = isprime(p) && isprime(8*p+7) && ((p % 8)==7) && isprime((p-7)/8); \\ _Michel Marcus_, Oct 16 2013

%Y Cf. A023231 Numbers n such that n and 8n + 7 are both prime.

%K nonn

%O 1,1

%A _Zak Seidov_, Mar 14 2009