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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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3
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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; refs; listen; history; internal format)
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OFFSET
| 1,9
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COMMENTS
| Also, the number of integers k in {1,2,...,n-1} such that k*n is square. - John W. Layman, Sep 08 2011
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FORMULA
| a(n) =A000188(n)-1.
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EXAMPLE
| 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
| Cf. A005117, A133466.
Sequence in context: A176891 A109527 A186715 * A016380 A203945 A015692
Adjacent sequences: A057915 A057916 A057917 * A057919 A057920 A057921
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KEYWORD
| easy,nonn
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AUTHOR
| Henry Bottomley (se16(AT)btinternet.com), Nov 22 2000
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