id:A131233 - 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
2

1, 2, 3, 4, 5, 5, 7, 8, 9, 9, 11, 10, 13, 13, 14, 16, 17, 15, 19, 18, 20, 21, 23, 20, 25, 25, 27, 26, 29, 22, 31, 32, 32, 33, 34, 30, 37, 37, 38, 36, 41, 32, 43, 42, 42, 45, 47, 40, 49, 45, 50, 50, 53, 45, 54, 52, 56, 57, 59, 44, 61, 61, 60, 64, 64, 52, 67, 66, 68, 58, 71, 60, 73 (list; graph; listen)

	OFFSET	`1,2`
	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 20 positive integers only 10 and 20 are divisible by both 2 and 5. There are 18 other positive integers <= 20, so a(20)=18.`
	CROSSREFS	`Cf. A131232.` `Adjacent sequences: A131230 A131231 A131232 this_sequence A131234 A131235 A131236` `Sequence in context: A082081 A008475 A073137 this_sequence A136623 A031218 A092762`
	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 October 7 14:39 EDT 2008. Contains 144666 sequences.

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