OFFSET
1,1
COMMENTS
This is a subsequence of A237659.
Conjecture: The sequence has infinitely many terms.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..1000 (n = 1..150 from Zhi-Wei Sun)
EXAMPLE
a(1) = 59 with 59, pi(59) = 17, pi(pi(59)) = pi(17) = 7 and pi(59^2) = 487 all prime.
MATHEMATICA
p[m_]:=PrimeQ[PrimePi[m^2]]
n=0; Do[If[p[Prime[Prime[Prime[k]]]], n=n+1; Print[n, " ", Prime[Prime[Prime[k]]]]], {k, 1, 1000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Feb 11 2014
STATUS
approved