A116999 - OEIS

%I #17 Jul 13 2024 10:59:36

%S 11,15,17,23,27,47,231,457,1249,1529,2343,4693,5939,5997,8367,19855,

%T 21295,36583

%N Numbers k such that 2^k - prime(k)^2 is prime.

%C No more terms below 30000. - _Giovanni Resta_, Apr 03 2006

%C No more terms below 130000. - _Michael S. Branicky_, Jul 13 2024

%e 15 is in the sequence because the 15th prime is 47 and 2^15 - 47^2 = 30559 is prime.

%p a:=proc(n) if isprime(2^n-ithprime(n)^2) then n else fi end: seq(a(n),n=1..1600); # _Emeric Deutsch_, Apr 06 2006

%t Select[Range[6000], PrimeQ[2^# - Prime[#]^2] &] (* _Michael De Vlieger_, Feb 02 2019 *)

%o (PARI) for(i=1,2000,if(isprime(2^i-prime(i)^2),print1(i,",")))

%K hard,more,nonn

%O 1,1

%A Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 03 2006

%E Corrected and extended by _Giovanni Resta_, Apr 03 2006

%E a(18) from _Michael S. Branicky_, Jun 23 2023