A349748 Primes p for which 2^p-1 and 5^p-1 are not relatively prime.

2, 179, 239, 359, 419, 431, 499, 547, 571, 641, 659, 719, 761, 937, 1013, 1019, 1223, 1439, 1499, 1559, 1789, 2039, 2339, 2399, 2459, 2539, 2593, 2677, 2699, 2819, 2939, 3299, 3359, 3539, 3779, 4013, 4019, 4273, 4513, 4787, 4919, 5039, 5279, 5393, 5399, 5639, 6173, 6199, 6899, 7079, 8599, 8741, 8929, 9059, 9419, 9479

Offset: 1

Author

Antti Karttunen, Nov 30 2021

Keywords

• nonn

Comments

Primes p for which A270390(p) = gcd(A000225(p), A024049(p)) > 1.

Examples

			2 is included as 2^2 - 1 = 3 and 5^2 - 1 = 24 share a prime factor 3.
		

Crossrefs

Cf. A000225, A024049, A270390.

Programs

Mathematica

upto=10^4;Select[Prime[Range[PrimePi[upto]]],GCD[2^#-1,5^#-1]>1&] (* Paolo Xausa, Nov 30 2021 *)

PARI

isA349748(n) = (isprime(n)&&(gcd(2^n-1,5^n-1)>1));

Python

from math import gcd
from sympy import isprime
def ok(n): return isprime(n) and gcd(2**n-1, 5**n-1) > 1
print([k for k in range(9500) if ok(k)]) # Michael S. Branicky, Nov 30 2021