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A077090
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When iteration of f[]=Phi[](Sigma[]-Phi[]) is started at initial values listed here it ends up in a cycle.
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7
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36, 40, 48, 50, 52, 60, 64, 66, 72, 76, 78, 80, 81, 84, 88, 90, 92, 96, 98, 100, 102, 105, 106, 108, 110, 112, 114, 116, 117, 118, 120, 122, 123, 124, 126, 128, 130, 132, 135, 136, 138, 140, 141, 142, 144, 146, 147, 148, 150, 152, 154, 156, 159, 160, 162, 164
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| n=22: nestlist = 105,[48,36,78]; n=72: nestlist = 72,108,120,160,156,168,[144,280,192]; below 2000 only these two cycles of length 3 appeared.
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MATHEMATICA
| f[x_] := EulerPhi[DivisorSigma[1, x]-EulerPhi[x]] Do[s=NestList[f, n, 100]; s1=Part[s, 98]; s2=Part[s, 99]; s3=Part[s, 100]; If[ !Equal[s1, s2], k=k+1; Print[{k, n, s1, s2, s3}]], {n, 2, 1000}]
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CROSSREFS
| Cf. A077091-A077100.
Sequence in context: A181457 A129288 A083248 * A067672 A181484 A060292
Adjacent sequences: A077087 A077088 A077089 * A077091 A077092 A077093
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Oct 31 2002
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