cp's OEIS Frontend

A368549 a(n) is the least k such that the greatest prime less than n*k is less than n times the greatest prime < k.

%I A368549 #6 Dec 30 2023 23:19:00
%S A368549 8,12,24,24,20,18,38,14,54,30,138,98,152,90,84,80,240,504,68,200,354,
%T A368549 854,224,1020,230,180,510,542,524,522,368,968,578,1098,1130,3462,744,
%U A368549 504,1218,1988,468,938,812,758,684,4002,2592,642,3120,4458,2958,3272,4920,572,5060,3300,14490,3188,6012
%N A368549 a(n) is the least k such that the greatest prime less than n*k is less than n times the greatest prime < k.
%C A368549 a(n) = p + 1 where p is the first prime such that there are no primes between n*p and n*(p+1).
%H A368549 Robert Israel, <a href="/A368549/b368549.txt">Table of n, a(n) for n = 2..280</a>
%e A368549 a(4) = 24 because the greatest prime < 24 is 23 and the greatest prime < 4*24 is 89 < 4*23.
%p A368549 f:= proc(n) local p;
%p A368549    p:= 1;
%p A368549    do
%p A368549      p:= nextprime(p);
%p A368549      if not ormap(isprime, [$ (n*p+1) .. (n*p+n-1)]) then return p+1 fi
%p A368549    od
%p A368549 end proc:
%p A368549 map(f, [$2..100]);
%Y A368549 Cf. A367035.
%K A368549 nonn
%O A368549 2,1
%A A368549 _Robert Israel_, Dec 29 2023