OFFSET
1,1
LINKS
Hiroaki Yamanouchi, Table of n, a(n) for n = 1..54
EXAMPLE
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.
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]; c+d-e-f==b]; Do[If[g[n]==True, Print[n]], {n, 1, 10^5}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Jan 24 2002
EXTENSIONS
Edited by Dean Hickerson and Robert G. Wilson v, Jan 26 2002
a(23)-a(26) from Donovan Johnson, Jan 02 2009
a(27)-a(30) from Hiroaki Yamanouchi, Sep 20 2014
STATUS
approved