OFFSET
1,2
FORMULA
a(n) = Sum_{d|sigma(n)} moebius(d)*floor(n/d). - Ridouane Oudra, May 12 2024
EXAMPLE
Among the positive integers not exceeding 12, the five numbers 1,3,5,9,11 are relatively prime to sigma(12)=28. Hence a(12)=5.
MAPLE
with(numtheory) : seq(add(mobius(d)*floor(n/d), d in divisors(sigma(n))) , n=1..100) ; # Ridouane Oudra, May 12 2024
MATHEMATICA
r = {}; Do[ s = DivisorSigma[1, n]; j = 0; For[i = 1, i <= n, i++, If[GCD[s, i] == 1, j++ ]]; r = Append[r, j], {n, 1, 10^2}]; r
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Joseph L. Pe, Jul 14 2002
STATUS
approved