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

%I A349748 #8 Dec 04 2021 12:30:46
%S A349748 2,179,239,359,419,431,499,547,571,641,659,719,761,937,1013,1019,1223,
%T A349748 1439,1499,1559,1789,2039,2339,2399,2459,2539,2593,2677,2699,2819,
%U A349748 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
%N A349748 Primes p for which 2^p-1 and 5^p-1 are not relatively prime.
%C A349748 Primes p for which A270390(p) = gcd(A000225(p), A024049(p)) > 1.
%e A349748 2 is included as 2^2 - 1 = 3 and 5^2 - 1 = 24 share a prime factor 3.
%t A349748 upto=10^4;Select[Prime[Range[PrimePi[upto]]],GCD[2^#-1,5^#-1]>1&] (* _Paolo Xausa_, Nov 30 2021 *)
%o A349748 (PARI) isA349748(n) = (isprime(n)&&(gcd(2^n-1,5^n-1)>1));
%o A349748 (Python)
%o A349748 from math import gcd
%o A349748 from sympy import isprime
%o A349748 def ok(n): return isprime(n) and gcd(2**n-1, 5**n-1) > 1
%o A349748 print([k for k in range(9500) if ok(k)]) # _Michael S. Branicky_, Nov 30 2021
%Y A349748 Cf. A000225, A024049, A270390.
%K A349748 nonn
%O A349748 1,1
%A A349748 _Antti Karttunen_, Nov 30 2021