A372491 Indices k such that A002533(k) is prime.

2, 3, 4, 5, 11, 17, 32, 53, 103, 107, 109, 113, 137, 197, 233, 811, 7993, 9281, 14387, 26573, 51361

Offset: 1

Author

Robert Israel, May 03 2024

Keywords

• nonn
• more

Comments

All terms are either primes or powers of 2.

Examples

			a(3) = 4 is a term because A002533(4) = 73 is prime.
		

Crossrefs

Cf. A002533, A111011.

Programs

Maple

B[0]:= 1: B[1]:= 1: R:= NULL: count:= 0:
for n from 2 while count < 18 do
  B[n]:= 2*B[n-1]+5*B[n-2];
  if (isprime(n) or n = 2^padic:-ordp(n,2)) and isprime(A[n]) then
    R:= R,n; count:= count+1
  fi
od:
R;

Mathematica

Flatten[Position[LinearRecurrence[{2, 5}, {1, 1}, 1000] ,Integer?PrimeQ]-1] (* _James C. McMahon, May 06 2024 *)

Formula

A111011(n) = A002533(a(n)).

Extensions

a(21) from Michael S. Branicky, May 04 2024