1,1

a(6) > 1199999, if it exists. - Karl-Heinz Hofmann, Jul 27 2021

Table of n, a(n) for n=1..5.

7 is a term because (2^7-2)/7 - 1 = 17 is prime.

(PARI) is(p) = isprime(p) && ispseudoprime((2^p-2)/p-1) \\ Jinyuan Wang, May 15 2021

Cf. A064535, A344360.

Sequence in context: A196309 A196281 A196331 * A159019 A059394 A176960

Adjacent sequences: A344358 A344359 A344360 * A344362 A344363 A344364

nonn,more

Jorge Coveiro, May 15 2021

a(5) from Hugo Pfoertner, May 17 2021

approved