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%I #15 May 06 2024 12:30:52
%S 2,3,4,5,11,17,32,53,103,107,109,113,137,197,233,811,7993,9281,14387,
%T 26573,51361
%N Indices k such that A002533(k) is prime.
%C All terms are either primes or powers of 2.
%F A111011(n) = A002533(a(n)).
%e a(3) = 4 is a term because A002533(4) = 73 is prime.
%p B[0]:= 1: B[1]:= 1: R:= NULL: count:= 0:
%p for n from 2 while count < 18 do
%p B[n]:= 2*B[n-1]+5*B[n-2];
%p if (isprime(n) or n = 2^padic:-ordp(n,2)) and isprime(A[n]) then
%p R:= R,n; count:= count+1
%p fi
%p od:
%p R;
%t Flatten[Position[LinearRecurrence[{2, 5}, {1, 1}, 1000] ,_Integer?PrimeQ]-1] (* _James C. McMahon_, May 06 2024 *)
%Y Cf. A002533, A111011.
%K nonn,more
%O 1,1
%A _Robert Israel_, May 03 2024
%E a(21) from _Michael S. Branicky_, May 04 2024