OFFSET
1,2
LINKS
Harry J. Smith, Table of n, a(n) for n=1..1000
EXAMPLE
The sequence includes squares, twice squares (such as 162 and 648), and other numbers (such as 48 and 180). The sigma_4/sigma_2 quotients usually have more than one distinct prime factor. Exception: sigma_4(48)/sigma_2(48) = 5732210/3410 = 1681 = 41^2.
MATHEMATICA
Do[s=DivisorSigma[4, n]; z=DivisorSigma[2, n]; If[IntegerQ[s/z]&&!PrimeQ[s/z], Print[n]], {n, 1, 10000}]
PROG
(PARI) { n=0; for (m=1, 10^9, if (frac(f=sigma(m, 4)/sigma(m, 2)), next); if (!isprime(f), write("b066112.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Feb 01 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 06 2001
EXTENSIONS
Edited by Jon E. Schoenfield, Dec 24 2016
STATUS
approved