OFFSET
1,4
COMMENTS
a(n) = omega(n) = 1 iff n is prime.
Not all positive integers are terms of this sequence as many are not expressible as the sum of products defined by the sequence, for example 2, 3, and 6.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
Wikipedia, Dirichlet convolution
MAPLE
with(numtheory):
a:= n-> add(sigma(d)*nops(factorset(n/d)), d=divisors(n)):
seq(a(n), n=1..100); # Alois P. Heinz, Jan 28 2019
MATHEMATICA
Table[DivisorSum[n, DivisorSigma[1, #] PrimeNu[n/#] &], {n, 71}] (* Michael De Vlieger, Jan 27 2019 *)
PROG
(PARI) a(n) = sumdiv(n, d, sigma(d)*omega(n/d)); \\ Michel Marcus, Jan 22 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Torlach Rush, Jan 18 2019
STATUS
approved