A361680 - OEIS

%I #10 Mar 22 2023 08:17:16

%S 3,7,11,31,47,67,83,163,179,193,263,367,389,499,563,571,887,967,1229,

%T 1087,1367,1873,1289,2647,1907,2083,1979,2557,2267,3697,2909,3121,

%U 3761,4507,4373,4723,5279,5857,6359,6793,7727,8167,7853,6823,6779,8059,9479,10567

%N The n-th prime p such that p + 2^n is also prime.

%C This sequence is non-monotonic: a(19) = 1229 > a(20) = 1087.

%H Alois P. Heinz, <a href="/A361680/b361680.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A361679(n,n).

%p b:= proc() option remember; local f; f:= proc() [] end;

%p       proc(n, k) option remember; local p;

%p         p:= `if`(nops(f(k))=0, 1, f(k)[-1]);

%p         while nops(f(k))<n do p:= nextprime(p);

%p           if isprime(p+2^k) then f(k):= [f(k)[], p] fi

%p         od; f(k)[n]

%p       end

%p     end():

%p a:= n-> b(n$2):

%p seq(a(n), n=1..55);

%Y Main diagonal of A361679.

%Y Cf. A000040.

%K nonn

%O 1,1

%A _Alois P. Heinz_, Mar 20 2023