A087509 - OEIS

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A087509

#{0<=k<=n: mod(kn,3)=2 }.

0, 0, 1, 0, 1, 2, 0, 2, 3, 0, 3, 4, 0, 4, 5, 0, 5, 6, 0, 6, 7, 0, 7, 8, 0, 8, 9, 0, 9, 10, 0, 10, 11, 0, 11, 12, 0, 12, 13, 0, 13, 14, 0, 14, 15, 0, 15, 16, 0, 16, 17, 0, 17, 18, 0, 18, 19, 0, 19, 20, 0, 20, 21, 0, 21, 22, 0, 22, 23, 0, 23, 24, 0, 24, 25, 0, 25, 26, 0, 26, 27, 0, 27, 28, 0, 28 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,6`
	COMMENTS	`A087507(n)+A087508(n)+A087509(n)=A000027(n)`
	FORMULA	`a(n)=sum{k=0..n, if (mod(kn, 3)=2, 1, 0}; a(n)=n-2(floor(n/3)+1)(1-cos(2pin/3))/3-floor(n/3)(5+4cos(2pin/3))/3.`
	EXAMPLE	`a(8)=#{1,4,7}=3.`
	CROSSREFS	`Sequence in context: A127954 A198061 A160706 * A181871 A089596 A105805` `Adjacent sequences: A087506 A087507 A087508 * A087510 A087511 A087512`
	KEYWORD	`easy,nonn`
	AUTHOR	`Paul Barry (pbarry(AT)wit.ie), Sep 11 2003`

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Last modified February 14 17:10 EST 2012. Contains 205644 sequences.