%I
%S 1,3,6,9,16,21,30,36,46,61,68,86,99,110,126,146,168,184,205,223,242,
%T 270,292,321,360,381,404,429,446,477,546,574,614,637,693,717,762,804,
%U 842,890,935,965,1029,1059,1105,1134,1222,1304,1348,1381,1423,1483
%N Greatest k such that (kth prime) <= (n times nth prime).
%C Might be roughly n^2/2 (seems to be marginally more at least for small n).
%H Michel Marcus, <a href="/A057855/b057855.txt">Table of n, a(n) for n = 1..5000</a>
%F a(n) = pi(n*prime(n)).
%e a(4)=9 since 4th prime is 7, 4*7=28, greatest prime less than or equal to 28 is 23 which is the 9th prime.
%p a:= n> numtheory[pi](n*ithprime(n)):
%p seq(a(n), n=1..61); # _Alois P. Heinz_, Aug 30 2019
%t Table[PrimePi[w*Prime[w]], {w, 1, 100}]
%o (PARI) a(n) = primepi(n*prime(n)); \\ _Michel Marcus_, Aug 30 2019
%Y Cf. A020900, A020901, A020934A020940, A033286 (n*prime(n)).
%K nonn
%O 1,2
%A _Henry Bottomley_, Nov 13 2000
