A116535 - OEIS

%I #13 Apr 16 2021 04:35:32

%S 3,7,5,7,5,3,5,5,3,3,3,3,5,3,3,5,5,3,5,3,3,3,3,3,3,3,3,3,5,3,5,3,3,3,

%T 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,5,3,3,3,3,3,3,3,3,3,3,3,5,

%U 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,5,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3

%N a(n) is the smallest odd prime p such that 2^n + p is not prime.

%C The sequence is bounded, namely {a(n)} = {3, 5, 7}, because one of the numbers 2^n + 3, 2^n + 5, 2^n + 7 is divisible by 3. - _Thomas Ordowski_, Apr 11 2019

%H Amiram Eldar, <a href="/A116535/b116535.txt">Table of n, a(n) for n = 0..10000</a>

%e A000079(20) + a(20) = 1048576 + 3 = 1048579 = 7*163*919.

%t Table[p := 2; While[PrimeQ[2^n + Prime[p]], p++ ]; Prime[p], {n, 0, 150}] (* _Stefan Steinerberger_, Mar 28 2006 *)

%Y Cf. A000079, A000040.

%K nonn

%O 0,1

%A _Reinhard Zumkeller_, Mar 27 2006

%E More terms from _Stefan Steinerberger_, Mar 28 2006