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A098186
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If f[x]=(sum of unitary-proper divisors of x)=A063919[x] is iterated, the iteration may lead to a fixed point which is either 0 or belongs to A002827, a unitary-perfect-number >1: 6,60,90,87360... Sequence gives initial values for which the iteration ends in 87360, the 4th unitary perfect number.
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3
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87360, 232608, 356640, 465144, 527712, 565728, 713208, 1018248, 1055352, 1211352, 1240032, 1303728, 1316904, 1352568, 1357584, 1360416, 1379280, 1550472, 1690440, 1835592, 2035608, 2078328, 2110632, 2262892, 2422632
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..25.
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EXAMPLE
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Iteration list started from n=1018248: {1018248, 1055352, 527712, 232608, 87360, 87360...}
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MATHEMATICA
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di[x_] :=Divisors[x]; ta={{0}}; ud[x_] :=Part[di[x], Flatten[Position[GCD[di[x], Reverse[di[x]]], 1]]]; asu[x_] :=Apply[Plus, ud[x]]-x; nsf[x_, ho_] :=NestList[asu, x, ho] Do[g=n; s=Last[NestList[asu, n, 100]]; If[Equal[s, 87360], Print[{n, s}]; ta=Append[ta, n]], {n, 1, 5000000}]; ta = Delete[ta, 1]
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CROSSREFS
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Cf. A063919, A002827, A063991, A097024, A097030-A097037, A098185.
Sequence in context: A237410 A206632 A230489 * A069313 A022207 A251907
Adjacent sequences: A098183 A098184 A098185 * A098187 A098188 A098189
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KEYWORD
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nonn
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AUTHOR
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Labos Elemer, Aug 31 2004
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STATUS
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approved
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