A067198 Numbers n such that sigma(n) = phi(n) + phi(n-1).

5, 7, 77, 6293, 12943, 23495, 30191, 99695, 147407, 240425, 258401, 535601, 1103825, 1570145, 1637867, 1972607, 2219135, 2241281, 2970517, 3785951, 5612321, 5917003, 6215951, 9249241, 9281899, 12496429, 14779531, 25739701, 30367321, 33522251, 33852841

Offset

1,1

Links

Table of n, a(n) for n=1..31.

Example

sigma(5) = 6 = 4 + 2 = phi(5) + phi(5-1), so 5 is a term of the sequence.

Mathematica

Select[Range[2, 10^5], EulerPhi[ # ] + EulerPhi[ # - 1] == DivisorSigma[1, # ] &]

Crossrefs

Cf. A000010, A000203.

Sequence in context: A098967 A107140 A141746 * A340468 A351636 A062583

Adjacent sequences: A067195 A067196 A067197 * A067199 A067200 A067201

Keyword

nonn

Author

Joseph L. Pe, Feb 19 2002

Extensions

a(9)-a(31) from Donovan Johnson, Mar 01 2012

Status

approved