OFFSET
1,2
COMMENTS
a(26) > 3*10^10. - Donovan Johnson, Mar 05 2014
EXAMPLE
phi(sigma(11)) + sigma(phi(11)) = phi(12) + sigma(10) = 4 + 18 = 2*11, so 11 is in the sequence.
MATHEMATICA
f[n_] := EulerPhi[DivisorSigma[1, n]]+DivisorSigma[1, EulerPhi[n]]; Select[Range[1, 10^5], f[ # ]==2*#&]
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Joseph L. Pe, Jan 25 2002
EXTENSIONS
Edited by Dean Hickerson, Jan 26 2002
a(20)-a(25) from Donovan Johnson, Sep 16 2009
a(26)-a(28) from Kevin P. Thompson, Apr 19 2022
a(29) from Kevin P. Thompson, Sep 04 2022
STATUS
approved