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A074887 Numbers n such that sigma(n - phi(n)) = phi(n + phi(n)). 0
915, 12957, 20745, 26985, 54621, 97785, 111615, 188013, 191775, 197631, 231045, 258687, 428745, 565761, 726645, 793653, 807639, 829857, 941451, 1048719, 1084587, 1224111, 1233027, 1863255, 1920681, 1973805, 2043489, 2129883, 2254119, 2265417, 2300151 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..31.

EXAMPLE

sigma(915-phi(915)) = sigma(915-480) = 720; phi(915+phi(915)) = phi(1395) = 720, so 915 is a term of the sequence.

MATHEMATICA

r = {}; Do[e = EulerPhi[n]; If[DivisorSigma[1, n - e] == EulerPhi[n + e], r = Append[r, n]], {n, 1, 10^5}]; r

Select[Range[3000000], DivisorSigma[1, #-EulerPhi[#]]==EulerPhi[#+ EulerPhi[ #]]&] (* Harvey P. Dale, Sep 03 2013 *)

CROSSREFS

Sequence in context: A286214 A189182 A252427 * A234993 A234764 A282592

Adjacent sequences: A074884 A074885 A074886 * A074888 A074889 A074890

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Sep 13 2002

EXTENSIONS

More terms from Harvey P. Dale, Sep 03 2013

STATUS

approved

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Last modified November 28 12:20 EST 2022. Contains 358416 sequences. (Running on oeis4.)