OFFSET
1,1
COMMENTS
Numbers n such that sigma(n) | n/2(n+1-phi(n)).
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..100
EXAMPLE
18/2*(19-phi(18)) = 117, sigma(18) = 39 and 117 / 39 = 3.
MAPLE
with(numtheory); P:=proc(q) local a, n;
for n from 1 to q do a:=n/2*(n+1-phi(n)); if type(a/sigma(n), integer) then print(n);
fi; od; end: P(10^6);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Mar 12 2014
EXTENSIONS
a(14)-a(31) from Giovanni Resta, Mar 12 2014
STATUS
approved