OFFSET
1,1
COMMENTS
First 5 terms from MathOverflow.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..91 (terms < 10^11)
Sylvain Julien, MathOverflow: rad(sigma(n)) = 2*rad(n)
MATHEMATICA
rad[n_] := Times @@ Transpose[FactorInteger[n]][[1]]; Select[Range[1000000], rad[DivisorSigma[1, #]] == 2*rad[#] &]
PROG
(PARI) rad(n)= my(p=factor(n)[, 1]); prod(i=1, length(p), p[i]);
isok(n) = rad(sigma(n)) == 2*rad(n); \\ Michel Marcus, Feb 28 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Feb 27 2014
EXTENSIONS
More terms from Michel Marcus, Feb 28 2014
STATUS
approved