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A127652
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Integers whose unitary aliquot sequences are longer than their ordinary aliquot sequences.
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4
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25, 28, 36, 40, 50, 68, 70, 74, 94, 95, 98, 116, 119, 134, 142, 143, 154, 162, 170, 175, 182, 189, 190, 200, 220, 226, 242, 245, 262, 273
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OFFSET
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1,1
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COMMENTS
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Here the length of an aliquot sequence is defined to be the length of the transient part of its trajectory + the length of its terminal cycle.
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REFERENCES
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Riele, H. J. J. te; Unitary Aliquot Sequences. MR 139/72, Mathematisch Centrum, 1972, Amsterdam.
Riele, H. J. J. te; Further Results On Unitary Aliquot Sequences. NW 2/73, Mathematisch Centrum, 1973, Amsterdam.
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LINKS
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FORMULA
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EXAMPLE
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a(5)=50 because the fifth integer whose unitary aliquot sequence is longer than its ordinary aliquot sequence is 50.
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MATHEMATICA
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UnitaryDivisors[n_Integer?Positive]:=Select[Divisors[n], GCD[ #, n/# ]==1&]; sstar[n_]:=Plus@@UnitaryDivisors[n]-n; g[n_] := If[n > 0, sstar[n], 0]; UnitaryTrajectory[n_] := Most[NestWhileList[g, n, UnsameQ, All]]; s[n_]:=DivisorSigma[1, n]-n; h[n_] := If[n > 0, s[n], 0]; OrdinaryTrajectory[n_] := Most[NestWhileList[h, n, UnsameQ, All]]; Select[Range[275], Length[UnitaryTrajectory[ # ]]>Length[OrdinaryTrajectory[ # ]] &]
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CROSSREFS
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Cf. A127161, A127162, A127163, A127164, A063769, A063990, A097032, A098007, A097010, A127653, A098185, A127654, A063991, A127655, A097037, A097036.
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KEYWORD
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hard,nonn
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AUTHOR
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STATUS
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approved
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