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A112751
Number of numbers of the form 3^i*5^j that are less than or equal to n.
2
1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10
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
Sequence in context: A334097 A122027 A359121 * A316843 A331246 A331256
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 18 2005
STATUS
approved