

A356478


a(n) is the least k such that there are exactly n primes p <= k such that 2*kp and p*(2*kp)+2*k are also prime.


1



2, 4, 11, 15, 21, 35, 42, 111, 81, 117, 126, 60, 291, 147, 225, 417, 210, 330, 357, 555, 561, 375, 315, 477, 735, 552, 420, 975, 630, 585, 816, 840, 930, 1925, 1302, 1170, 1140, 2202, 1215, 1155, 1911, 1551, 2031, 1590, 1365, 2136, 1425, 2562, 1740, 1485, 2331, 2790, 2160, 2100, 2640, 2010, 3681, 2400, 1785, 2262, 3252, 2622, 2940, 1575, 2310, 2541, 3987, 2772
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OFFSET

0,1


COMMENTS

a(n) is the least k such that A356864(k) = n.


LINKS



EXAMPLE

a(3) = 15 because there are exactly 3 primes p <= 15 with 30p and p*(30p)+30 prime, namely 7, 11 and 13, and no smaller number works.


MAPLE

f:= proc(n) local p, q, t;
p:= 1: t:= 0:
do
p:= nextprime(p);
q:= np;
if q <= p then return t fi;
if isprime(q) and isprime(p*q+n) then t:= t+1 fi;
od
end proc:
V:= Array(0..100): V[0]:= 2: count:= 1:
for nn from 2 while count < 101 do
v:= f(2*nn);
if v > 100 then next fi;
if V[v] = 0 then count:= count+1; V[v]:= nn; fi;
od:
convert(V, list);


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



