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A190613 a(n) = Sum_{k=1..n} (-1)^(n-floor(n/k)) * floor(n/k). 1
0, 1, 1, 5, 4, 6, 2, 12, 12, 11, 1, 21, 17, 9, 7, 37, 18, 16, 10, 28, 30, 30, -6, 52, 48, 11, 17, 59, 19, 39, 9, 53, 65, 27, 9, 83, 44, 30, 10, 98, 54, 28, 36, 50, 68, 82, -34, 128, 98, 13, 49, 91, 47, 59, 21, 119, 85, 71, -11, 129, 107, 15, 49, 153, 92, 72, 24, 110, 68, 120, -24, 166, 166, -20 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..73.

MATHEMATICA

Table[Sum[(-1)^(n-Floor[n/k] ) Floor[n/k], {k, n}], {n, 0, 80}] (* Harvey P. Dale, May 01 2018 *)

PROG

(PARI) a(n)=sum(k=1, n, (-1)^(n-n\k)*(n\k))

CROSSREFS

Cf. A059851, A006218.

Sequence in context: A092426 A255291 A070365 * A161011 A232734 A298513

Adjacent sequences:  A190610 A190611 A190612 * A190614 A190615 A190616

KEYWORD

sign

AUTHOR

Franklin T. Adams-Watters, May 14 2011

STATUS

approved

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Last modified December 15 17:03 EST 2019. Contains 330000 sequences. (Running on oeis4.)