A182154 -id:A182154 - cp's OEIS frontend

A358621 Smallest b > 1 such that b^(2^n)+1 is a Sophie Germain prime.

2, 2, 160, 140, 2800, 8660, 62150, 4085530, 922820, 4629490, 5802710, 1146175000, 90894850

Offset: 0

Graph
List
Refs
Listen
History
Text
Internal format

Jeppe Stig Nielsen, Nov 23 2022

nonn
hard
more

In other words, 2*b^(2^n)+3 is also prime.

For n > 1, a(n) ends in 0 because b is even (or else b^(2^n)+1 would have 2 as a proper divisor) and b == 0 (mod 5) (or else 2*b^(2^n)+3 would have 5 as a proper divisor).

PrimeGrid and "Stream", GFN-1x Small Primes search, mentions a(12).

Cf. A005384, A056993, A182154.

a(n)=n<2&&return(2);forstep(b=10,+oo,10,ispseudoprime(b^(2^n)+1)&&ispseudoprime(2*b^(2^n)+3)&&return(b))

cp's OEIS Frontend

A358621 Smallest b > 1 such that b^(2^n)+1 is a Sophie Germain prime.

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

PARI