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A066939
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Numbers n such that phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = phi(n) + sigma(n).
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2
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13954, 106899, 307835, 783201, 979731, 2980255, 9266817, 18479215, 49062925, 109044425, 114029313, 120914101, 185480686, 218223299, 347941741, 429365395, 466423743, 492508289, 610803875, 895938847, 993189741, 1093958383
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| For n = 13954, phi(phi(n)) + sigma(sigma(n)) - phi(sigma(n)) - sigma(phi(n)) = phi(6976) + sigma(20934) - phi(20934) - sigma(6976) = 3456 + 45396 - 6972 - 13970 = 27910 = 6976 + 20934 = phi(n) + sigma(n), so 13954 is in the sequence.
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MATHEMATICA
| 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]; a+b==c+d-e-f]; Do[If[g[n]==True, Print[n]], {n, 1, 10^6}]
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CROSSREFS
| Cf. A000010, A000203, A066850, A066945, A066946.
Sequence in context: A190817 A118464 A031819 * A140708 A066698 A157786
Adjacent sequences: A066936 A066937 A066938 * A066940 A066941 A066942
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 24 2002
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EXTENSIONS
| Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Jan 26 2002
a(8)-a(22) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jan 02 2009
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