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).

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

Links

Table of n, a(n) for n=1..25.

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

Cf. A000010, A047994.

Sequence in context: A293029 A298761 A062133 * A050684 A073214 A293356

Adjacent sequences: A329726 A329727 A329728 * A329730 A329731 A329732

Keyword

nonn,more

Author

Amiram Eldar, Nov 19 2019

Extensions

a(18)-a(25) from Giovanni Resta, Nov 20 2019

Status

approved