A063685 - OEIS

%I #22 Aug 19 2024 20:52:37

%S 2,3,4,5,11,20,85,212,4925

%N Numbers k such that !k + phi(k) - 1 is prime.

%C a(10) > 5000. - _J.W.L. (Jan) Eerland_, Nov 19 2022

%C a(10) > 13469. - _J.W.L. (Jan) Eerland_, Nov 20 2022

%C a(10) > 30000. - _Michael S. Branicky_, Aug 19 2024

%t n=1;Monitor[Parallelize[While[True,If[PrimeQ[Sum[Factorial[k],{k,0,n-1}]+EulerPhi[n]-1],Print[n]];n++];n],n] (* _J.W.L. (Jan) Eerland_, Nov 19 2022 *)

%o (PARI) f(n) = sum(k=0,n-1,k!); \\ A003422

%o for(n=1,10^6, if(isprime(f(n)+eulerphi(n)-1),print(n)))

%Y Cf. A003422.

%K nonn,more

%O 1,1

%A _Jason Earls_, Aug 22 2001

%E a(9) from _J.W.L. (Jan) Eerland_, Nov 19 2022