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A072490 Number of squarefree numbers (excluding 1) less than n. 1
0, 0, 1, 2, 2, 3, 4, 5, 5, 5, 6, 7, 7, 8, 9, 10, 10, 11, 11, 12, 12, 13, 14, 15, 15, 15, 16, 16, 16, 17, 18, 19, 19, 20, 21, 22, 22, 23, 24, 25, 25, 26, 27, 28, 28, 28, 29, 30, 30, 30, 30, 31, 31, 32, 32, 33, 33, 34, 35, 36, 36, 37, 38, 38, 38, 39 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..66.

FORMULA

a(n) = A013928(n) - 1, n > 1.

G.f.: (x/(1 - x)) * Sum_{k>=2} mu(k)^2*x^k. - Ilya Gutkovskiy, Sep 14 2019

EXAMPLE

a(10) = 5 as the squarefree numbers less than 10 are 2,3,5,6 and 7.

PROG

(PARI) a(n) = sum(k=2, n, issquarefree(k)); \\ Michel Marcus, Sep 15 2019

CROSSREFS

Cf. A005117, A013928, A144338.

Sequence in context: A081094 A054633 A327982 * A242493 A261345 A243285

Adjacent sequences:  A072487 A072488 A072489 * A072491 A072492 A072493

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Jul 14 2002

EXTENSIONS

Name clarified and more terms from Ilya Gutkovskiy, Sep 14 2019

STATUS

approved

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Last modified July 5 06:34 EDT 2020. Contains 335459 sequences. (Running on oeis4.)