OFFSET
1,1
COMMENTS
5*10^12 < a(26) <= 9318208204800. Also terms: 11007398707200, 37664679628800, 600328733921280. - Giovanni Resta, Nov 20 2019
EXAMPLE
20 is in the sequence since phi(20) = 8, uphi(20) = 12 and 8 + 12 = 20.
MATHEMATICA
uphi[1] = 1; uphi[n_] := Times @@ (-1 + Power @@@ FactorInteger[n]);
aQ[n_] := EulerPhi[n] + uphi[n] == n; Select[Range[2*10^6], aQ]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Nov 19 2019
EXTENSIONS
a(18)-a(25) from Giovanni Resta, Nov 20 2019
STATUS
approved