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A110196 Numbers n such that k=2n is the least k such that phi(n+k)=2*phi(k). 1
1, 13, 23, 97, 113, 131, 199, 227, 491, 859, 929 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

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

MATHEMATICA

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

CROSSREFS

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

KEYWORD

nonn

AUTHOR

T. D. Noe, Jul 15 2005

STATUS

approved

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Last modified April 13 20:44 EDT 2021. Contains 342941 sequences. (Running on oeis4.)