A101040 - OEIS

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A101040

If n has one or two prime-factors then 1 else 0.

0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,1`
	COMMENTS	`a(A033942(n))=0; for n>1: a(A037143(n))=1;` `a(A000040(n))=1; a(A001358(n))=1;` `A101041(n) = Sum(a(k): 1<=k<=n) + 1.`
	LINKS	`Table of n, a(n) for n=1..105.` `Index entries for characteristic functions`
	FORMULA	`a(n) = A010051(n)+A064911(n) = 0^floor(A001222(n)/3)-0^(n-1).`
	CROSSREFS	`Sequence in context: A106549 A075897 A135947 * A175629 A109720 A022932` `Adjacent sequences: A101037 A101038 A101039 * A101041 A101042 A101043`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller, Nov 28 2004`
	STATUS	`approved`

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Last modified May 21 10:17 EDT 2013. Contains 225478 sequences.