A157684 - OEIS

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A157684

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

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

	OFFSET	`1,5`
	COMMENTS	`Presumably a(n)=n/3+o(n)`
	FORMULA	`a(n)=sum(k=1,n,(K(k+1)-1)*(K(k+1)-K(k))) where K(k)=A000002(k).`
	PROG	`(PARI) a(n)=sum(k=1, n, if(abs(A000002(k)-1)+abs(A000002(k+1)-2), 0, 1))`
	CROSSREFS	`Cf. A157685, A157686, A157687` `Sequence in context: A194327 A058032 A056155 * A194339 A194335 A026099` `Adjacent sequences: A157681 A157682 A157683 * A157685 A157686 A157687`
	KEYWORD	`nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 04 2009`

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Last modified February 15 13:13 EST 2012. Contains 205791 sequences.