A066516 - OEIS

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A066516

Numbers n such that g(sigma(n)) = phi(n), where g(n) = prime(n+1) - prime(n).

1, 4, 5, 15, 18, 30, 36

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OFFSET

1,2

COMMENTS

No more terms below 10^6. - Robert G. Wilson v, Jan 05 2002

No more terms below 2 * 10^17. - Charles R Greathouse IV, Feb 15 2011

On the Riemann hypothesis, a(7) = 36 is the last member of this sequence. - Charles R Greathouse IV, Feb 15 2011

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

g(sigma(4)) = g(7) = prime(8)-prime(7) = 19-17 = 2 = phi(4).

MATHEMATICA

g[x_] := Prime[x + 1] - Prime[x]; Select[Range[1, 10^5], g[DivisorSigma[1, # ]] == EulerPhi[ # ] &]

CROSSREFS

Sequence in context: A257311 A369790 A330857 * A047184 A002509 A230983

Adjacent sequences: A066513 A066514 A066515 * A066517 A066518 A066519

KEYWORD

nonn,fini,full

AUTHOR

Joseph L. Pe, Jan 04 2002

STATUS

approved