A207575 Numbers k such that phi(k) + 2 divides k + 2 and k is not twice a prime.

1, 390, 10374, 2283934267736070, 7316037865689066623729670

Offset: 1

Author

José María Grau Ribas, Feb 19 2012

Keywords

• nonn
• more
• hard

Comments

Contains 2 * terms t of A350777 such that (t-3)/phi(t) = 2. - Max Alekseyev, Oct 26 2023

Crossrefs

Cf. A000010, A207574, A202855, A203966, A350777.

Programs

Mathematica

Select[Range[20000000], !PrimeQ[#/2] && Divisible[#+2, EulerPhi[#]+2]&]

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

Extensions

a(4)-a(5) from Max Alekseyev, Nov 06 2023