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A092586 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. 2
7, 87, 231, 463, 617, 691, 751, 855, 1059, 1127, 2795, 4819, 11999, 18527, 22481, 75311, 121939, 232901, 256751, 288883, 313919, 371519, 845831, 1285841, 1762799, 1815167, 7195199, 9096191, 40324121, 93070943, 99388823, 113140151, 238072223, 487394063 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
(sigma(phi(x))-phi(sigma(x)))/(x+1) equals 1 if x=7; is 2 if x=463; is 3 if x=4819.
MATHEMATICA
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
CROSSREFS
Sequence in context: A220306 A344106 A346987 * A048363 A254473 A183613
KEYWORD
nonn
AUTHOR
Labos Elemer, Mar 01 2004
EXTENSIONS
Edited and extended by Robert G. Wilson v, Mar 03 2004
a(33)-a(34) from Donovan Johnson, Mar 04 2013
STATUS
approved

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Last modified March 28 13:19 EDT 2024. Contains 371254 sequences. (Running on oeis4.)