OFFSET
1,2
COMMENTS
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..48 (terms < 10^12)
EXAMPLE
sigma(39^2)/39^2 = 61/39 = 2379 = sigma(39^2), so 39 is a term.
MATHEMATICA
Select[Range[10^6], GCD[#^2, DivisorSigma[1, #^2]] == # &] (* Giovanni Resta, Jun 10 2016 *)
PROG
(PARI) isok(n) = {ab = sigma(n^2)/n^2; numerator(ab)*denominator(ab) == sigma(n^2); }
(PARI) {isa(n) = if( n<1, 0, n == gcd(n^2, sigma(n^2)))}; /* Michael Somos, Nov 26 2014 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 26 2014
EXTENSIONS
New name after Michael Somos by Michel Marcus, Nov 27 2014
a(13)-a(14) from Michel Marcus, Nov 27 2014
a(15)-a(26) from Giovanni Resta, Jun 10 2016
STATUS
approved