1,2

No other n < 10^6. Note that all n>1 are primes.

Table of n, a(n) for n=1..11.

Do[k=1; While[EulerPhi[n+k] != 2*EulerPhi[k], k++ ]; If[k==2n, Print[n]], {n, 5000}]

Cf. A050473 (least k such that phi(n+k)=2*phi(k)).

Sequence in context: A155093 A147443 A131447 * A039448 A299361 A089768

Adjacent sequences: A110193 A110194 A110195 * A110197 A110198 A110199

nonn

T. D. Noe, Jul 15 2005

approved