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

1,1

Comments

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

Links

Table of n, a(n) for n=1..56.

Example

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

Mathematica

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

Prog

(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

Crossrefs

Cf. A000225, A024049, A270390.

Sequence in context: A103427 A216355 A139942 * A239548 A272237 A094221

Adjacent sequences: A349745 A349746 A349747 * A349749 A349750 A349751

Keyword

nonn

Author

Antti Karttunen, Nov 30 2021

Status

approved