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A066946
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Numbers n such that phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = sigma(n).
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2
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827, 975, 1607, 13149, 20919, 34921, 58649, 202223, 347869, 545377, 900521, 1451135, 2288845, 2453509, 2804855, 3063031, 4134579, 11320177, 11446955, 14573651, 16477307, 17678225, 25164429, 27514643, 28475077, 47443799
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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..26.
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EXAMPLE
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Let n = 827. Then phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = phi(826) + sigma(828) - phi(828) - sigma(826) = 348 + 2184 - 264 - 1440 = 828 = sigma(n), so 827 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==b]; Do[If[g[n]==True, Print[n]], {n, 1, 10^5}]
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CROSSREFS
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Cf. A000010, A000203, A066850, A066939, A066945.
Sequence in context: A057002 A051989 A104375 * A143799 A046496 A102350
Adjacent sequences: A066943 A066944 A066945 * A066947 A066948 A066949
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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) and Robert G. Wilson v, Jan 26 2002
a(23)-a(26) from Donovan Johnson, Jan 02 2009
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STATUS
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approved
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