OFFSET
1,2
COMMENTS
The sum of the aliquot divisors of a prime is exactly 1. - Martin Renner, Oct 13 2011
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Donovan Johnson)
EXAMPLE
a(4) = 56: the aliquot divisors 1,2,4,7,8,14,28 sum to 64, a cube.
MAPLE
a := []; for n from 1 to 1000 do if sigma(n) <> n+1 and type( simplify((sigma(n)-n)^(1/3)), `integer`) then a := [op(a), n]; fi; od: a;
MATHEMATICA
Select[Range[20000], !PrimeQ[#] && IntegerQ @ Surd[DivisorSigma[1, #] - #, 3] &] (* Amiram Eldar, Feb 23 2020 *)
PROG
(PARI) c=0; for(n=1, 13127239, if(isprime(n)==0, if(ispower(sigma(n)-n, 3), c++; write("b048698.txt", c " " n)))) /* Donovan Johnson, Mar 10 2013 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
STATUS
approved