A269544 Numbers n such that 7*8^n + 1 is prime.

2, 40, 58, 60, 130, 144, 752, 7462, 18162, 69028, 187272, 268178, 270410, 497284, 713304, 722600, 1005254

Offset

1,1

Comments

a(n) is even because 7*8^(2*k+1) + 1 is divisible by 3.

Links

Table of n, a(n) for n=1..17.

Formula

a(n) = A032353(n)/3 where this is an integer.

Mathematica

Select[Range[0, 200000, 2], PrimeQ[7*8^# + 1] &]

Prog

(PARI) is(n)=ispseudoprime(7*8^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A056799, A245241, A268061.

Sequence in context: A349717 A349726 A275547 * A281761 A370069 A359859

Adjacent sequences: A269541 A269542 A269543 * A269545 A269546 A269547

Keyword

nonn,hard,more

Author

Robert Price, Feb 29 2016

Status

approved