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Search: id:A057918
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| A057918 |
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Number of pairs of numbers (a,b) each less than n where (a,b,n) is in geometric progression. |
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+0
1
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| 0, 0, 0, 1, 0, 0, 0, 1, 2, 0, 0, 1, 0, 0, 0, 3, 0, 2, 0, 1, 0, 0, 0, 1, 4, 0, 2, 1, 0, 0, 0, 3, 0, 0, 0, 5, 0, 0, 0, 1, 0, 0, 0, 1, 2, 0, 0, 3, 6, 4, 0, 1, 0, 2, 0, 1, 0, 0, 0, 1, 0, 0, 2, 7, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 4, 1, 0, 0, 0, 3, 8, 0, 0, 1, 0, 0, 0, 1, 0, 2, 0, 1, 0, 0, 0, 3, 0, 6, 2, 9, 0, 0, 0, 1, 0
(list; graph; listen)
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OFFSET
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1,9
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FORMULA
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a(n) =A000188(n)-1.
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EXAMPLE
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a(72)=5 since (2,12,72), (8,24,72), (18,36,72), (32,48,72), (50,60,72) are the possible three term geometric progressions.
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CROSSREFS
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Sequence in context: A088534 A025441 A109527 this_sequence A016380 A015692 A016232
Adjacent sequences: A057915 A057916 A057917 this_sequence A057919 A057920 A057921
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KEYWORD
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easy,nonn
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AUTHOR
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Henry Bottomley (se16(AT)btinternet.com), Nov 22 2000
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