A339868 - OEIS

%I #8 Dec 21 2020 02:05:06

%S 2,7,29,61,83,109,293,311,449,709,773,997,1021,1031,1103,1231,1297,

%T 1301,1381,1487,1523,1553,1559,1709,2089,2161,2221,2297,2339,2377,

%U 2521,2663,2677,2687,2711,2927,3037,3163,3167,3221,3407,3533,4091,4259,4729,5009,5189,5309,5581,6691,6899,7001,7297

%N Primes p such that p + A023896(p-1) and p + A023896(p+1) are prime.

%H Robert Israel, <a href="/A339868/b339868.txt">Table of n, a(n) for n = 1..10000</a>

%e a(3) = 29 is a term because 29, 29 + A023896(28) = 197 and 29 + A023896(30) = 149 are prime.

%p A023896:= n -> n*numtheory:-phi(n)/2:

%p A023896(1):= 1:

%p select(t -> isprime(t+A023896(t-1)) and isprime(t+A023896(t+1)),

%p [seq(ithprime(i),i=1..1000)]);

%Y Cf. A023896.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Dec 20 2020