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Search: id:A055155
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| A055155 |
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Sum_{k|n} [GCD(k,n/k)]. |
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+0
3
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| 1, 2, 2, 4, 2, 4, 2, 6, 5, 4, 2, 8, 2, 4, 4, 10, 2, 10, 2, 8, 4, 4, 2, 12, 7, 4, 8, 8, 2, 8, 2, 14, 4, 4, 4, 20, 2, 4, 4, 12, 2, 8, 2, 8, 10, 4, 2, 20, 9, 14, 4, 8, 2, 16, 4, 12, 4, 4, 2, 16, 2, 4, 10, 22, 4, 8, 2, 8, 4, 8, 2, 30, 2, 4, 14, 8, 4, 8, 2, 20, 17, 4, 2, 16, 4, 4, 4, 12, 2, 20, 4, 8, 4, 4
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(n) is odd iff n is odd square. - Vladeta Jovovic (vladeta(AT)Eunet.yu), Aug 27 2002
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FORMULA
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Multiplicative with a(p^e) = (p^(e/2)*(p+1)-2)/(p-1) for even e and a(p^e) = 2*(p^((e+1)/2)-1)/(p-1) for odd e. - Vladeta Jovovic (vladeta(AT)Eunet.yu), Nov 01 2001
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EXAMPLE
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a(9) = GCD(1,9) + GCD(3,3) + GCD(9,1) = 5, since 1, 3, 9 are the positive divisors of 9.
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CROSSREFS
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Cf. A057670.
Adjacent sequences: A055152 A055153 A055154 this_sequence A055156 A055157 A055158
Sequence in context: A129089 A124315 A101113 this_sequence A085191 A061142 A091248
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KEYWORD
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easy,nonn,mult
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Jul 02 2000
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EXTENSIONS
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More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jul 04 2000
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