OFFSET
1,1
LINKS
Carl R. White, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
n=12: Sum_divisors (1,2,3,4,6,12) = 28; Sum_prime_factors (2,2,3) =7 -> 28/7 = 4. n=319: Sum_divisors (1,11,29,319) = 360; Sum_prime_factors (11,29) =40 -> 360/40 = 9.
MAPLE
with(numtheory); P:=proc(q) local a, n;
for n from 2 to q do if not isprime(n) then a:=ifactors(n)[2];
if type(sigma(n)/add(a[k][1]*a[k][2], k=1..nops(a)), integer) then print(n);
fi; fi; od; end: P(10^4);
MATHEMATICA
Select[Range[2, 600], Divisible[DivisorSigma[1, #], Total[ Times@@@ FactorInteger[#]]]&] (* Harvey P. Dale, Dec 09 2010 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, Jun 23 2009
EXTENSIONS
Offset corrected by R. J. Mathar, Jun 26 2009
STATUS
approved