A157685 - OEIS

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A157685

a(n)=#{1<=k<=n : [K(k),K(k+1)]=[2,1]} where K=A000002

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

	OFFSET	`1,6`
	COMMENTS	`Presumably a(n)=n/3+o(n)`
	FORMULA	`a(n)=sum(k=1,n,(1-K(k))*(K(k+1)-K(k))) where K(k)=A000002(k).`
	PROG	`(PARI) a(n)=sum(k=1, n, if(abs(A000002(k)-2)+abs(A000002(k+1)-1), 0, 1))`
	CROSSREFS	`Cf. A157684, A157686, A157687` `Sequence in context: A099741 A047743 A062299 * A127757 A172264 A079001` `Adjacent sequences: A157682 A157683 A157684 * A157686 A157687 A157688`
	KEYWORD	`nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 04 2009`

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Last modified February 14 09:47 EST 2012. Contains 205614 sequences.