A333364 Indices of primes p whose order of primeness A078442(p) is prime.

2, 3, 7, 11, 13, 17, 19, 23, 29, 37, 41, 43, 47, 53, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283

Offset: 1

Author

Alois P. Heinz, Mar 16 2020

Keywords

• nonn

Comments

All terms are prime.

Examples

			11 is a term: prime(11) = 31 -> 11 -> 5 -> 3 -> 2 -> 1, five (a prime number of) steps "->" = pi = A000720.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000
• N. Fernandez, An order of primeness, F(p)
• N. Fernandez, An order of primeness [cached copy, included with permission of the author]

Crossrefs

Cf. A000040, A000720, A049076, A333353.

Programs

Maple

b:= proc(n) option remember;
      `if`(isprime(n), 1+b(numtheory[pi](n)), 0)
    end:
a:= proc(n) option remember; local p;
      p:= `if`(n=1, 1, a(n-1));
      do p:= nextprime(p);
         if isprime(b(p)+1) then break fi
      od; p
    end:
seq(a(n), n=1..62);

Mathematica

b[n_] := b[n] = If[PrimeQ[n], 1 + b[PrimePi[n]], 0];
a[n_] := a[n] = Module[{p}, p = If[n == 1, 1, a[n - 1]];
   While[True, p = NextPrime[p]; If[PrimeQ[b[p] + 1], Break[]]]; p];
Table[a[n], {n, 1, 62}] (* Jean-François Alcover, Sep 14 2022, after Alois P. Heinz *)

Formula

{ p in primes : A049076(p) is prime }.

a(n) = pi(A333353(n)), with pi = A000720.