id:A131232 - OEIS Search Results

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a(n) = number of positive integers < n which don't have 2 or more distinct prime divisors in common with n.

+0
3

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 12, 13, 14, 15, 16, 15, 18, 18, 20, 21, 22, 20, 24, 25, 26, 26, 28, 22, 30, 31, 32, 33, 34, 30, 36, 37, 38, 36, 40, 32, 42, 42, 42, 45, 46, 40, 48, 45, 50, 50, 52, 45, 54, 52, 56, 57, 58, 44, 60, 61, 60, 63, 64, 52, 66, 66, 68, 58, 70, 60, 72 (list; graph; listen)

	OFFSET	`1,3`
	EXAMPLE	`The distinct primes which divide 20 are 2 and 5. So a(20) is the number of positive integers < 20 which are not divisible by at least 2 distinct primes dividing 20; i.e. are not divisible by both 2 and 5. Among the first 19 positive integers only 10 is divisible by both 2 and 5. There are 18 other positive integers <= 19, so a(20)=18.`
	CROSSREFS	`Cf. A131233.` `Sequence in context: A122262 A017895 A130024 this_sequence A010881 A053832 A056961` `Adjacent sequences: A131229 A131230 A131231 this_sequence A131233 A131234 A131235`
	KEYWORD	`nonn`
	AUTHOR	`Leroy Quet (qq-quet(AT)mindspring.com), Jun 20 2007`
	EXTENSIONS	`More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jul 18 2007`

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Last modified August 29 17:54 EDT 2008. Contains 143238 sequences.

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