1,3

If p is prime, a(p) = p - phi(p - phi(p)) = p - phi(1) = p - 1. - Wesley Ivan Hurt, May 21 2021

Table of n, a(n) for n=1..73.

a(n) = n - A000010(A051953(n)).

Table[n - EulerPhi[n - EulerPhi[n]], {n, 100}]

Cf. A000010 (phi), A051953 (cototient).

Sequence in context: A061984 A337125 A063208 * A262265 A227683 A321166

Adjacent sequences: A343909 A343910 A343911 * A343913 A343914 A343915

nonn

Wesley Ivan Hurt, May 03 2021

approved