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A091531 Primes p such that k = 2p is the smallest positive solution to the equation phi(p+k) = phi(p) + phi(k), where phi is Euler's totient function. 1
7, 23, 31, 43, 59, 67, 71, 73, 101, 103, 107, 127, 131, 137, 139, 179, 199, 211, 223, 227, 239, 269, 281, 283, 307, 311, 331, 347, 359, 367, 379, 383, 431, 439, 463, 467, 479, 487, 491, 503, 523, 547, 563, 571, 607, 619, 631, 643, 659, 661, 683, 691, 719, 727 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Note that for all primes p > 3, phi(3p) = phi(p) + phi(2p).

LINKS

Table of n, a(n) for n=1..54.

MATHEMATICA

lst={}; Do[p=Prime[n]; k=1; While[EulerPhi[p+k]!=EulerPhi[p]+EulerPhi[k], k++ ]; If[k==2p, AppendTo[lst, p]], {n, 3, 200}]; lst

CROSSREFS

Cf. A066426 (least k such that phi(n+k)=phi(n)+phi(k)).

Sequence in context: A095087 A144517 A225185 * A036259 A004628 A089199

Adjacent sequences:  A091528 A091529 A091530 * A091532 A091533 A091534

KEYWORD

nonn

AUTHOR

T. D. Noe, Jan 19 2004

STATUS

approved

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Last modified May 25 17:06 EDT 2020. Contains 334595 sequences. (Running on oeis4.)