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Search: id:A066850
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| A066850 |
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Numbers n such that phi(phi(n)) + sigma(sigma(n)) = phi(sigma(n)) + sigma(phi(n)), where phi=A000010 is Euler's totient function and sigma=A000203 is the sum of divisors function. |
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4
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| 1, 4, 2669, 9559, 15293, 32583, 36593, 38443, 255367, 257239, 273977, 283391, 314101, 421553, 488363, 532975, 768699, 839973, 871757, 1960479, 2337221, 2374867, 3084659, 3326653, 3735029, 4440017, 5387373, 7930439, 8114377
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OFFSET
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1,2
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EXAMPLE
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Let n = 2669. Then phi(phi(n)) + sigma(sigma(n)) = phi(2496) + sigma(2844) = 768 + 7280 = 8048 and phi(sigma(n)) + sigma(phi(n)) = phi(2844) + sigma(2496) = 936 + 7112 = 8048. So 2669 is in the sequence.
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MATHEMATICA
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g[x_] := Module[{a, b, c, d, e, f}, a = EulerPhi[x]; b = DivisorSigma[1, x]; c = EulerPhi[a]; d = DivisorSigma[1, b]; e = EulerPhi[b]; f = DivisorSigma[1, a]; c + d - e - f]; Do[If[g[n] == 0, Print[n]], {n, 1, 10^6}]
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CROSSREFS
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Sequence in context: A047676 A079187 A131587 this_sequence A066837 A132639 A132643
Adjacent sequences: A066847 A066848 A066849 this_sequence A066851 A066852 A066853
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 24 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jan 24 2002
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