OFFSET
1,3
FORMULA
From Ridouane Oudra, Jul 29 2019: (Start)
a(n) = Card_{ k | A003593(k) <= n }.
a(n) = Sum_{k=1..n} mu(15*k)*floor(n/k), where mu is the Möbius function (A008683).
a(n) = Sum_{k=1..n} (floor(15^k/k)-floor((15^k-1)/k)). (End)
From Ridouane Oudra, Jul 17 2020: (Start)
a(n) = Sum_{i=0..floor(log_5(n))} (floor(log_3(n/5^i)) + 1).
a(n) = Sum_{i=0..floor(log_3(n))} (floor(log_5(n/3^i)) + 1). (End)
MAPLE
with(numtheory): seq(add(mobius(15*k)*floor(n/k), k=1..n), n=1..90); # Ridouane Oudra, Jul 29 2019
PROG
(Magma) [&+[MoebiusMu(15*k)*Floor(n/k):k in [1..n]]: n in [1..97]]; // Marius A. Burtea, Jul 30 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 18 2005
STATUS
approved