A271633 Numbers k such that sigma(phi(k)) - phi(k) = phi(sigma(k)), where phi(k) is the Euler totient function of k and sigma(k) is the sum of the divisors of k.

21, 350, 366, 532, 702, 1072, 5264, 7128, 23604, 24102, 30222, 30636, 32142, 32274, 34350, 47338, 70722, 78530, 113550, 137214, 197316, 235624, 292206, 357490, 367704, 398346, 406596, 453096, 453264, 464820, 479880, 485460, 504966, 509124, 512430, 519870, 539220

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..215 (terms below 10^9)

Example

sigma(phi(21)) - phi(21) = 28 - 12 = 16 = phi(sigma(21)).

Maple

with(numtheory): P:= proc(q) local n; for n from 1 to q do
if sigma(phi(n))-phi(n)=phi(sigma(n)) then print(n); fi;
od; end: P(10^6);

Mathematica

Select[Range[10^6], DivisorSigma[1, #] - # &@ EulerPhi@ # == EulerPhi@ DivisorSigma[1, #] &] (* Michael De Vlieger, Apr 21 2016 *)

Prog

(PARI) isok(k) = my(x=eulerphi(k)); sigma(x) - x == eulerphi(sigma(k)); \\ Michel Marcus, Jul 13 2019

Crossrefs

Cf. A000010, A000203, A001065, A033632, A062401.

Sequence in context: A299813 A299688 A300320 * A184289 A192093 A006105

Adjacent sequences: A271630 A271631 A271632 * A271634 A271635 A271636

Keyword

nonn

Author

Paolo P. Lava, Apr 19 2016

Status

approved