OFFSET
1,2
COMMENTS
If n is a k-multiperfect, then a(n) = k.
LINKS
Allan C. Wechsler, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
a249670[n_Integer] := Numerator[DivisorSigma[-1, n]]*Denominator[DivisorSigma[-1, n]]; a249670 /@ Range[80] (* Michael De Vlieger, Nov 10 2014 *)
PROG
(PARI) a(n) = my(ab = sigma(n)/n); numerator(ab)*denominator(ab);
(Haskell)
a249670 n = div (n * s) (gcd n s ^ 2)
where s = sum (filter (\k -> mod n k == 0) [1..n])
-- Allan C. Wechsler, Mar 31 2023
CROSSREFS
Cf. A000203 (sigma(n)).
KEYWORD
nonn
AUTHOR
Michel Marcus, Nov 03 2014
STATUS
approved