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A069143
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a(1) = a(2) = 1; a(n) = sigma(a(n-1)+a(n-2)).
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0
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1, 1, 3, 7, 18, 31, 57, 180, 320, 1092, 2478, 10368, 25704, 100800, 393120, 1965600, 10326624, 39657600, 131580288, 511223790, 1469266560, 4911616440, 22120488000, 95841111600, 460020244320, 2163425531904, 9805180170240
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OFFSET
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1,3
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LINKS
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MATHEMATICA
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a[1] = a[2] = 1; a[n_] := a[n] = DivisorSigma[1, a[n - 1] + a[n - 2]]; Table[a[n], {n, 27}]
RecurrenceTable[{a[1]==a[2]==1, a[n]==DivisorSigma[1, a[n-1]+a[n-2]]}, a, {n, 30}] (* Harvey P. Dale, Feb 15 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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