OFFSET
1,1
FORMULA
a(n) = Sum_{d|n} f(n/d)*mu(d), where f(n) = A002110(n).
EXAMPLE
For n=3, a(3) = moebius(1)*primorial(3) + moebius(3)*primorial(1) = 30*1 + 2*(-1) = 30 - 28 = 2.
MATHEMATICA
a[n_] := DivisorSum[n, Product[Prime[i], {i, 1, #}] * MoebiusMu[n/#] &]; Array[a, 17] (* Amiram Eldar, Aug 22 2023 *)
PROG
(PARI) primorial(n) = prod(i=1, n, prime(i));
a(n) = sumdiv(n, d, moebius(d)*primorial(n/d)); \\ Michel Marcus, Apr 05 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 19 2001
EXTENSIONS
a(18)-a(19) from Amiram Eldar, Aug 22 2023
STATUS
approved