A066155 - OEIS

A066155

Numbers k such that phi(k) = sigma(k+1) - sigma(k-1).

4, 6, 11, 32, 38, 54, 84, 278, 407, 804, 1854, 2664, 3287, 6579, 11327, 14750, 15608, 20720, 41664, 46839, 70190, 73283, 80429, 185231, 241614, 275876, 355292, 375200, 410327, 511220, 692909, 763179, 901494, 920390, 1089984, 1099196, 1356759

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OFFSET

1,1

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..70

EXAMPLE

phi(6) = 2 = 8 - 6 = sigma(7) - sigma(5).

MATHEMATICA

Select [Range[1, 10^6], EulerPhi[ # ] == DivisorSigma[1, # + 1] - DivisorSigma[1, # - 1] & ]

PROG

(PARI) isok(k) = { k > 1 && eulerphi(k) == sigma(k + 1) - sigma(k - 1) } \\ Harry J. Smith, Feb 03 2010

CROSSREFS

Sequence in context: A285994 A290651 A358913 * A105308 A116983 A196271

Adjacent sequences: A066152 A066153 A066154 * A066156 A066157 A066158

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Dec 13 2001

EXTENSIONS

a(35)-a(37) from Harry J. Smith, Feb 03 2010

STATUS

approved