OFFSET
1,2
PROG
(PARI) is(n)=my(s=sigma(n), p=factor(s)[, 1], k); for(i=1, #p, k=s/p[i]; if(k<n&&n%k, return(0))); 1 \\ Charles R Greathouse IV, Mar 01 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 01 2017
EXTENSIONS
Corrected by Charles R Greathouse IV, Mar 01 2017
STATUS
approved