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A131233
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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.
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1
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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
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OFFSET
| 1,2
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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.
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CROSSREFS
| Cf. A131232.
Sequence in context: A161656 A162683 A073137 * A136623 A031218 A163382
Adjacent sequences: A131230 A131231 A131232 * A131234 A131235 A131236
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Jun 20 2007
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EXTENSIONS
| More terms from Joshua Zucker (joshua.zucker(AT)stanfordalumni.org), Jul 18 2007
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