A005087 - OEIS

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A005087

Number of distinct odd primes dividing n.

0, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 2, 0, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 0, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 0, 2, 2, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1, 2, 2, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 1, 2, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,15`
	COMMENTS	`a(n) = A001221(n) - 1 + n mod 2. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 03 2003`
	FORMULA	`Additive with a(p^e) = 0 if p = 2, 1 otherwise.`
	PROG	`(Sage)` `def A005087(n) : return len(filter(is_prime, divisors(n))) + n % 2 - 1` `[A005087(n) for n in (1..80)] # Peter Luschny, Feb 01 2012`
	CROSSREFS	`Cf. A087436.` `Sequence in context: A025905 A115861 A199322 * A050332 A029425 A025902` `Adjacent sequences: A005084 A005085 A005086 * A005088 A005089 A005090`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com).`
	EXTENSIONS	`More terms from Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 03 2003`

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Last modified February 16 11:51 EST 2012. Contains 205908 sequences.