

A356190


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.


1



2, 7, 11, 17, 23, 29, 31, 1, 37, 1, 53, 61, 59, 71, 79, 89, 1, 109, 97, 101, 1, 1, 127, 1, 137, 151, 149, 157, 1, 179, 1, 191, 1, 1, 211, 1, 1, 223, 233, 1, 251, 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
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OFFSET

1,1


LINKS



FORMULA

a(n) <= A168421(n+1)  2, with equality for n = 6, 263, 3061, 4750, 4893, 5029, 5555, 6101, ....


EXAMPLE

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.


MAPLE

V:= Vector(100, 1): p:= 1:
for n from 1 while p < 727 do # note that A168421(101) = 727
p:= nextprime(p);
v:= numtheory:pi(2*p)n;
if v <= 100 and V[v] = 1 then
V[v]:= p;
fi
od:
convert(V, list);


CROSSREFS



KEYWORD

sign


AUTHOR



STATUS

approved



