A340160 - OEIS

%I #7 Jan 06 2021 02:12:27

%S 283,43,2,11,31,71,167,179,601,359,419,1439,1559,3359,7559,6047,5039,

%T 13679,21001,13441,20161,45361,15121,10079,54001,41579,35281,92399,

%U 99793,92401,100801,65521,100799,196561,241919,377999,110879,451439,453601,478801,498961,383041,393121,262079,453599

%N a(n) is the least prime p such that there are exactly n primes of the form p+d where d is a divisor of p-1 or of p+1.

%H Robert Israel, <a href="/A340160/b340160.txt">Table of n, a(n) for n = 0..149</a>

%e a(3) = 11, with 3 primes of the form 11+t where t is a divisor of 10 or 12, namely 13 = 11+2, 17 = 11+6 and 23=11+12.

%p f:= proc(p)

%p      nops(select(t -> isprime(t+p), numtheory:-divisors(p-1) union numtheory:-divisors(p+1)))

%p end proc:

%p V:= Array(0..50):

%p count:= 0: p:= 1:

%p while count < 51 do

%p   p:= nextprime(p);

%p   v:= f(p);

%p   if v <= 50 and V[v]=0 then count:= count+1; V[v]:= p; fi

%p od:

%p convert(V,list);

%K nonn

%O 0,1

%A _J. M. Bergot_ and _Robert Israel_, Dec 29 2020