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