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A092585
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Numbers n such that sigma(phi(n))-phi(sigma(n)) is nonzero and is divisible by (n-1), that is A065395(n)/(n-1) = (phi(sigma(n))-sigma(phi(n)))/(n-1) is a nonzero integer.
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3
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2, 4, 16, 64, 151, 449, 3403, 4096, 4267, 9307, 35905, 65536, 247285, 262144, 17625601, 33126625, 399288961, 649232833, 947278081, 1073741824, 2102485441, 4555788385, 5203567081, 6103058177, 7115716609
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OFFSET
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1,1
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LINKS
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EXAMPLE
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(sigma(phi(x))-phi(sigma(x)))/(x-1) is -1 if x=2,4,16,64,4096,65536,262144 and is 2 if x=151,449,3403, etc.
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MATHEMATICA
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f[ x_] := EulerPhi[ DivisorSigma[1, x]] - DivisorSigma[1, EulerPhi[x]]; t = {}; Do[ s = f[n]; If[ s != 0 && Mod[ s, n - 1] == 0, Print[n]; AppendTo[t, n], {n, 2*10^8}]; t
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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