OFFSET
1,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1184
FORMULA
a(n) = Sum_{j=1..n} Sum_{d|j} 7^(d-1) * mu(j/d).
a(n) = A143327(n,7).
a(n) = Sum_{j=1..n} A143325(j,7).
a(n) = A143326(n,7) / 7.
G.f.: (1/(1 - x)) * Sum_{k>=1} mu(k) * x^k / (1 - 7*x^k). - Ilya Gutkovskiy, Dec 11 2020
MAPLE
b:= n-> add(`if`(d=n, 7^(n-1), -b(d)), d=numtheory[divisors](n)):
a:= proc(n) option remember; b(n)+`if`(n<2, 0, a(n-1)) end:
seq(a(n), n=1..30);
PROG
(PARI) a(n) = sum(j=1, n, sumdiv(j, d, 7^(d-1)*moebius(j/d))); \\ Michel Marcus, Dec 11 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 05 2018
STATUS
approved