A067226 Numbers k such that phi(5k+1) = sigma(k).

5005, 6745, 79695, 99145, 160195, 166135, 296065, 350935, 486805, 960355, 1291105, 1350745, 1817365, 2218645, 2445685, 3287680, 4069135, 5341375, 5497965, 8933085, 14495065, 15106795, 16824535, 16850995, 18510055, 18710125, 21309085, 21521500, 22453345

Offset

1,1

Comments

Are there any terms not congruent to 5 in the sequence?

a(58) = 104447959 is the first example. - Charles R Greathouse IV, Jan 29 2012

Links

Table of n, a(n) for n=1..29.

Mathematica

Select[Range[10^6], EulerPhi[5*# + 1] == DivisorSigma[1, #] &] (* Amiram Eldar, May 09 2022 *)

Prog

(PARI) for(n=1, 1e9, if(sigma(n)==eulerphi(5*n+1), print1(n", "))) \\ Charles R Greathouse IV, Jan 29 2012

Crossrefs

Cf. A000010, A000203, A067224, A067235.

Sequence in context: A108011 A018188 A280879 * A249081 A154059 A138637

Adjacent sequences: A067223 A067224 A067225 * A067227 A067228 A067229

Keyword

nonn

Author

Benoit Cloitre, Feb 20 2002

Extensions

a(11)-a(29) from Donovan Johnson, Jan 29 2012

Status

approved