OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson)
Kevin A. Broughan and Daniel Delbourgo, On the Ratio of the Sum of Divisors and Euler’s Totient Function I, Journal of Integer Sequences, Vol. 16 (2013), Article 13.8.8.
Kevin A. Broughan and Qizhi Zhou, On the Ratio of the Sum of Divisors and Euler's Totient Function II, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.2.
EXAMPLE
sigma(56) = 120 = 5*24 = 5*phi(56) so 56 is in the sequence.
MATHEMATICA
Do[If[DivisorSigma[1, m]==5*EulerPhi[m], Print[m]], {m, 1500000}]
PROG
(PARI) is(n)=sigma(n)==5*eulerphi(n) \\ Charles R Greathouse IV, May 09 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Jan 29 2008, Jan 30 2008
STATUS
approved