A182262 - OEIS

%I #20 Nov 05 2020 19:22:33

%S 3,5,5,5,17,7,17,7,7,7,59,19,17,13,7,19,137,13,19,7,23,97,19,89,17,

%T 223,29,109,5,19,5,59,197,5,17,307,59,83,109,157,19,23,43,109,103,7,

%U 23,19,7,269,43,13,5,67,89,83,479,53,53,383,7,83,113,37,5,23

%N Least prime p that 6^n - p is prime.

%H Robert Israel, <a href="/A182262/b182262.txt">Table of n, a(n) for n = 1..2035</a>

%e For n=3 p=5 is the least prime that 6^3-p is prime (211).

%p f:= proc(n) local t,p;

%p   t:= 6^n;

%p   p:= 2;

%p   do

%p     p:= nextprime(p);

%p   until isprime(t-p);

%p   p

%p end proc:

%p map(f, [$1..100]); # _Robert Israel_, Nov 05 2020

%t f[n_] := Block[{p = 2}, While[! PrimeQ[6^n - p], p = NextPrime[p]];

%t   p]; Array[f, 60]

%o (PARI) a(n) = my(p = 2); while(!isprime(6^n-p), p = nextprime(p+1)); p; \\ _Michel Marcus_, Mar 23 2016

%Y Cf. A013607, A059614 (n such that a(n)=5).

%K nonn

%O 1,1

%A _Mateusz Szymański_, Apr 21 2012