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A081973
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a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.
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3
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1, 2, 5, 11, 23, 47, 95, 215, 479, 959, 2063, 4127, 8255, 19007, 38327, 76655, 168647, 338663, 708263, 1453823, 3308543, 7154303, 14919599, 29910119, 59820239, 119676959, 239387375, 538142975, 1205440295, 2651968655, 6663140495
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OFFSET
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1,2
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COMMENTS
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a(n+1)/a(n) >= 2 for all n. Is a(n+1)/a(n) bounded? Up to n=160, the maximum value is a(31)/a(30)=2.5125261124174184479... - Benoit Cloitre, Apr 17 2003
a(n) == 23 (mod 24) for all n>=5. - Dean Hickerson (dean.hickerson(AT)yahoo.com), Apr 20 2003
a(n) = partial sums of A165929(n). [From Jaroslav Krizek, Sep 30 2009]
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..200
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MATHEMATICA
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a[1]=1; a[n_] := a[n]=a[n-1]+DivisorSigma[1, a[n-1]]
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CROSSREFS
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Sequence in context: A055010 A083329 A153893 * A055496 A105120 A084403
Adjacent sequences: A081970 A081971 A081972 * A081974 A081975 A081976
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 03 2003
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EXTENSIONS
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More terms from Gabriel Cunningham (gcasey(AT)mit.edu), Apr 07 2003
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STATUS
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approved
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