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A329729
Numbers k such that phi(k) + uphi(k) = k, where phi is the Euler totient function (A000010) and uphi is the unitary totient function (A047994).
0
2, 20, 36, 440, 1008, 2052, 20240, 86688, 116928, 192024, 354240, 1460160, 1902560, 42451200, 43007328, 77299200, 1595255040, 4556027520, 17973550080, 34221035520, 62863257600, 76146739200, 91506844800, 602152462080, 1106232422400
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
Sequence in context: A293029 A298761 A062133 * A050684 A073214 A293356
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Nov 19 2019
EXTENSIONS
a(18)-a(25) from Giovanni Resta, Nov 20 2019
STATUS
approved