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%I #25 Jul 22 2022 17:16:17
%S 1,2,3,4,5,6,7,8,9,10,12,14,17,18,25,29,32,33,34,35,39,40,44,45,47,48,
%T 50,52,56,58,60,65,66,70,72,78,81,83,84,87,89,90,94,104,105,107,112,
%U 115,116,123,130,140,144,156,161,162,164,165,166,168,174,176,178,180,181
%N Numbers k such that 1 + phi(k)^4 is a prime. Phi is Euler's totient function.
%C The sequence appears to be infinite, but I have no proof.
%H Dumitru Damian, <a href="/A180648/b180648.txt">Table of n, a(n) for n = 1..10000</a>
%e 35 is a term since 1 + phi(35)^4 = 1 + 24^4 = 331777 is prime.
%t Select[Range[200],PrimeQ[1+EulerPhi[#]^4]&] (* _Harvey P. Dale_, Jul 22 2022 *)
%o (Python)
%o from sympy import isprime, totient
%o print([n for n in range(1,10**3) if isprime(1+totient(n)**4)]) # _Dumitru Damian_, Jan 29 2022
%o (PARI) isok(k) = isprime(1+eulerphi(k)^4); \\ _Michel Marcus_, Jan 30 2022
%Y Cf. A000010, A000040, A002808, A018252.
%K nonn
%O 1,2
%A _Carmine Suriano_, Sep 14 2010
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