A366663 a(n) = phi(9^n-1), where phi is Euler's totient function (A000010).

4, 32, 288, 2560, 26400, 165888, 2384928, 15728640, 141087744, 1246080000, 14758128000, 85996339200, 1270928131200, 8810420097024, 70207948800000, 677066362060800, 8218041445152000, 43129128265187328, 674757689572915200, 4238841176064000000

Offset: 1

Author

Sean A. Irvine, Oct 15 2023

Keywords

• nonn

Links

• Max Alekseyev, Table of n, a(n) for n = 1..690

Crossrefs

phi(k^n-1): A053287 (k=2), A295500 (k=3), A295501 (k=4), A295502 (k=5), A366623 (k=6), A366635 (k=7), A366654 (k=8), this sequence (k=9), A295503 (k=10), A366685 (k=11), A366711 (k=12).

Cf. A000010, A024101, A057952, A366660, A366661, A366662, A366667.

Programs

Mathematica

EulerPhi[9^Range[30] - 1]

PARI

{a(n) = eulerphi(9^n-1)}

Formula

a(n) = A295500(2*n) = 2 * A295500(n) * A366579(n). - Max Alekseyev, Jan 07 2024