OFFSET
1,1
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..500
EXAMPLE
m=136, phi(136)=64, sigma(136)=270, product=17280, quotient=128; for primes the formula holds.
MAPLE
with(numtheory): select(m->modp(phi(m)*sigma(m), m-1)=0 and not isprime(m), [$2..40000]); # Muniru A Asiru, Jun 18 2018
MATHEMATICA
Do[s=EulerPhi[n]*DivisorSigma[1, n]; If[IntegerQ[s/(n-1)]&&!PrimeQ[n], Print[n]], {n, 1, 100000}]
PROG
(PARI) { n=0; for (m=2, 10^9, s=eulerphi(m)*sigma(m); if (s%(m-1) == 0 && !isprime(m), write("b065149.txt", n++, " ", m); if (n==500, return)) ) } \\ Harry J. Smith, Oct 12 2009
(GAP) Filtered([2..40000], m->Phi(m)*Sigma(m) mod (m-1)=0 and not IsPrime(m)); # Muniru A Asiru, Jun 18 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Oct 18 2001
EXTENSIONS
Offset changed from 0 to 1 by Harry J. Smith, Oct 12 2009
STATUS
approved