A195815 - OEIS

%I #22 Aug 25 2024 21:07:42

%S 1,2,3,5,11,188,509,1730,2571,3402,4407,9890,18609,20456,32529,38124,

%T 95087

%N Numbers k such that 2*(3^k-2*k)+1 is prime.

%C The associated primes are 3, 11, 43, 467, 354251,....

%e a(1)=1 because 2*(3^1-2*1)+1=3 is a prime, a(2)=2 because 2*(3^2-2*2)+1=11 is a prime, a(3)=3 because 2*(3^3-2*3)+1=43 is a prime, a(4)=5 because 2*(3^5-2*5)+1=467 is a prime, a(5)=11 because 2*(3^11-2*11)+1=354251 is a prime.

%o (PARI) is(n)=ispseudoprime(2*(3^n-2*n)+1) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A195732.

%K nonn,more

%O 1,2

%A _Juri-Stepan Gerasimov_, Sep 24 2011

%E a(9)-a(16) from _Michael S. Branicky_, Jul 15 2023

%E a(17) from _Michael S. Branicky_, Aug 25 2024