login
a(n) is the largest number such that pi(a(n)) = prime(n).
2

%I #15 Jun 30 2021 10:36:54

%S 4,6,12,18,36,42,60,70,88,112,130,162,180,192,222,250,280,292,336,358,

%T 372,408,432,462,520,556,568,592,600,618,718,742,786,808,862,880,928,

%U 970,996,1032,1068,1090,1162,1180,1212,1222,1300,1422,1438,1450,1480

%N a(n) is the largest number such that pi(a(n)) = prime(n).

%C Primes with prime subscripts correspond to least numbers m, such that pi(m) = prime(n).

%H Robert Israel, <a href="/A073123/b073123.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = Max{x: A000720(x)=A000040(n)}.

%F a(n) = A000040(A000040(n)+1) - 1.

%e n=25: prime(25)=97; for 12 terms X = {509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520}, pi(X)=97. Largest is a(25)=520, smallest is A006450(25), number of terms = A073124(25).

%p seq(ithprime(ithprime(n)+1)-1, n=1..100); # _Robert Israel_, May 14 2018

%Y Cf. A000720, A000040, A006450, A073124.

%Y Equals A072677(n) - 1.

%K nonn

%O 1,1

%A _Labos Elemer_, Jul 16 2002

%E Edited by _Robert Israel_, May 14 2018