A087508 - OEIS

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A087508

#{0<=k<=n: mod(kn,3)=1 }.

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

	OFFSET	`0,5`
	COMMENTS	`A087507(n)+A087508(n)+A087509(n)=A000027(n)`
	FORMULA	`a(n)=sum{k=0..n, if (mod(kn, 3)=1, 1, 0) }; a(n)=(2/3)(floor(n/3)+1)(1-cos(2pi*n/3)).`
	EXAMPLE	`a(4)=#{1,4}=2`
	CROSSREFS	`Sequence in context: A127465 A127899 A128615 * A095731 A048142 A071426` `Adjacent sequences: A087505 A087506 A087507 * A087509 A087510 A087511`
	KEYWORD	`easy,nonn`
	AUTHOR	`Paul Barry (pbarry(AT)wit.ie), Sep 11 2003`

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Last modified February 15 08:49 EST 2012. Contains 205740 sequences.