A037138 Numbers k such that sigma(totient(k)) + sigma(cototient(k)) = 2k.

26, 1114, 11832, 96288, 290544

Offset

1,1

Comments

Old title was: "a(n) = n-phi(n)-s(n-phi(n))=s(phi(n))-phi(n) or s(n-phi(n))-n+phi(n)=phi(n)-s(phi(n))." (Here s(n)=sigma(n)-n.)

Next term > 100000000. - Charlie Neder, Feb 21 2019

Links

Table of n, a(n) for n=1..5.

Eric Weisstein's World of Mathematics, Cototient

Prog

(PARI) isok(n) = (sigma(eulerphi(n)) + sigma(n-eulerphi(n))) == 2*n;
  \\ Charlie Neder, Feb 21 2019

Crossrefs

Cf. A000010, A051953. - Charlie Neder, Feb 21 2019

Sequence in context: A357376 A241874 A330497 * A091429 A200721 A187463

Adjacent sequences: A037135 A037136 A037137 * A037139 A037140 A037141

Keyword

more,nonn

Author

Naohiro Nomoto

Extensions

Offset set to 1 by Michel Marcus, Feb 03 2014

Title changed by Charlie Neder, Feb 21 2019

Status

approved