%I #9 Aug 18 2022 11:44:32
%S 2,7,11,17,23,29,31,1,37,1,53,61,59,71,79,89,1,109,97,101,1,1,
%T 127,1,137,151,149,157,1,179,1,191,1,1,211,1,1,223,233,1,251,
%U 257,263,293,1,1,1,1,307,311,1,1,1,331,349,347,367,373,379,389,409,1,1,419,1,431,443
%N a(n) is the least prime p such that there are exactly n primes strictly between p and 2*p, or 1 if there is no such p.
%H Robert Israel, <a href="/A356190/b356190.txt">Table of n, a(n) for n = 1..9999</a>
%F a(n) <= A168421(n+1)  2, with equality for n = 6, 263, 3061, 4750, 4893, 5029, 5555, 6101, ....
%e a(3) = 11 because there are exactly 3 primes between 11 and 22, namely 13, 17 and 19, and 11 is the least prime that works.
%p V:= Vector(100,1): p:= 1:
%p for n from 1 while p < 727 do # note that A168421(101) = 727
%p p:= nextprime(p);
%p v:= numtheory:pi(2*p)n;
%p if v <= 100 and V[v] = 1 then
%p V[v]:= p;
%p fi
%p od:
%p convert(V,list);
%Y Cf. A168421.
%K sign
%O 1,1
%A _J. M. Bergot_ and _Robert Israel_, Jul 29 2022
