OFFSET
1,2
COMMENTS
Sum of the divisors of n of the form p, p^2, p*q, p^3, p^2*q, or p*q*r where p,q,r are primes.
FORMULA
a(n) = Sum_{d|n} (d * Sum_{k=1..3} [Omega(d) = k]), where [ ] is the Iverson bracket.
MAPLE
f:= n -> convert(select(t -> numtheory:-bigomega(t)<=3, numtheory:-divisors(n)), `+`)-1:
map(f, [$1..100]); # Robert Israel, Dec 26 2021
MATHEMATICA
a[n_] := DivisorSum[n, # &, 0 < PrimeOmega[#] <= 3 &]; Array[a, 100] (* Amiram Eldar, Dec 26 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Dec 25 2021
STATUS
approved