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Search: id:A158974
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| A158974 |
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a(n) = count of numbers k <= n such that not all proper divisors of k are divisors of n. |
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3
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| 0, 0, 0, 0, 1, 0, 2, 1, 3, 3, 5, 1, 6, 5, 6, 6, 9, 6, 10, 7, 10, 11, 13, 7, 14, 14, 15, 14, 18, 12, 19, 16, 19, 20, 21, 16, 24, 23, 24, 20, 27, 22, 28, 25, 25, 29, 31, 23, 32, 30, 33, 32, 36, 31, 36, 32, 38, 39, 41, 31, 42, 41, 39, 40, 44, 41, 47, 44, 47, 43, 50, 40, 51, 50, 49, 50
(list; graph; listen)
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OFFSET
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1,7
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COMMENT
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For primes p, a(p) = p - A036234(p) = p - A000720(p) - 1.
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EXAMPLE
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For n = 8 we have the following proper divisors for k <= n: {1}, {1}, {1}, {1, 2}, {1}, {1, 2, 3}, {1}, {1, 2, 4}. Only k = 6 has a proper divisor that is not a divisor of 8, viz. 3. Hence a(8) = 1.
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PROGRAM
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(MAGMA) [ #[ k: k in [1..n] | exists(t){ d: d in Divisors(k) | d ne k and d notin Divisors(n) } ]: n in [1..76] ];
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CROSSREFS
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Cf. A000040, A036234, A000720, A158973.
Sequence in context: A038071 A032140 A032044 this_sequence A152993 A026927 A074500
Adjacent sequences: A158971 A158972 A158973 this_sequence A158975 A158976 A158977
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KEYWORD
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nonn
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AUTHOR
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Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Apr 01 2009
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EXTENSIONS
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Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Apr 06 2009
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