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A275495 a(n) = Sum_{k=2..n} floor(n/k) - 2*floor(n/(2*k)). 3
0, 1, 2, 2, 3, 4, 5, 4, 6, 7, 8, 7, 8, 9, 12, 10, 11, 12, 13, 12, 15, 16, 17, 14, 16, 17, 20, 19, 20, 21, 22, 19, 22, 23, 26, 24, 25, 26, 29, 26, 27, 28, 29, 28, 33, 34, 35, 30, 32, 33, 36, 35, 36, 37, 40, 37, 40, 41, 42, 39, 40, 41, 46, 42, 45, 46, 47, 46, 49 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = Sum_{i=1..n} floor((n-i)/i)*(-1)^(i+1). - Wesley Ivan Hurt, Sep 13 2017

MATHEMATICA

Table[Sum[Floor[n/k] - 2*Floor[n/(2*k)], {k, 2, n}], {n, 1, 50}] (* G. C. Greubel, Jul 30 2016 *)

PROG

(Sage)

print [sum([floor(n/k) - 2*floor(n/(2*k)) for k in (2..n)]) for n in (1..69)]

(PARI) a(n)=sum(k=2, n, n\k) - 2*sum(k=2, n\2, n\(2*k)) \\ Charles R Greathouse IV, Jul 30 2016

CROSSREFS

Cf. A002541, row sums of A275510.

Sequence in context: A224401 A252462 A094457 * A022820 A292259 A241397

Adjacent sequences:  A275492 A275493 A275494 * A275496 A275497 A275498

KEYWORD

nonn,easy

AUTHOR

Peter Luschny, Jul 30 2016

STATUS

approved

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Last modified October 23 10:16 EDT 2019. Contains 328345 sequences. (Running on oeis4.)