|
%I #31 Nov 06 2023 11:28:23
%S 1,390,10374,2283934267736070,7316037865689066623729670
%N Numbers k such that phi(k) + 2 divides k + 2 and k is not twice a prime.
%C Contains 2 * terms t of A350777 such that (t-3)/phi(t) = 2. - _Max Alekseyev_, Oct 26 2023
%t Select[Range[20000000], !PrimeQ[#/2] && Divisible[#+2, EulerPhi[#]+2]&]
%o (PARI) for(n=1,1e5,if((n+2)%(eulerphi(n)+2)==0&&(n%2||!isprime(n/2)), print1(n", "))) \\ _Charles R Greathouse IV_, Mar 02 2012
%Y Cf. A000010, A207574, A202855, A203966, A350777.
%K nonn,more,hard
%O 1,2
%A _José María Grau Ribas_, Feb 19 2012
%E a(4)-a(5) from _Max Alekseyev_, Nov 06 2023
|
