A067243 Numbers m such that sigma(m+1)+sigma(m-1) = 6*phi(m).

34, 55, 141, 322, 664, 988, 1149, 1505, 2230, 2631, 2906, 2912, 8559, 11194, 18215, 18754, 57104, 60599, 62881, 64604, 78759, 81580, 96304, 96944, 97220, 98944, 99164, 126520, 182495, 192417, 200123, 220661, 255968, 272405, 275931, 354032, 392755, 422956, 426095, 444962

Offset

1,1

Links

Table of n, a(n) for n=1..40.

Mathematica

Select[Range[200000], DivisorSigma[1, #-1]+DivisorSigma[1, #+1] == 6*EulerPhi[#]&] (* Harvey P. Dale, May 07 2014 *)

Prog

(PARI) isok(m) = (m>1) && (sigma(m+1)+sigma(m-1) == 6*eulerphi(m)); \\ Michel Marcus, Feb 17 2021

Crossrefs

Cf. A000010, A000203, A067242.

Sequence in context: A305061 A051969 A241520 * A171668 A259676 A227304

Adjacent sequences: A067240 A067241 A067242 * A067244 A067245 A067246

Keyword

easy,nonn

Author

Benoit Cloitre, Feb 20 2002

Extensions

More terms from Michel Marcus, Feb 17 2021

Status

approved