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%I #18 Feb 28 2024 13:21:08
%S 1,4,40,288,3072,23600,259200,1847104,21523360,152845056,1700870400,
%T 12550120000,130459631616,997562438080,11159367815680,81159501312000,
%U 926510094425920,6670865700716544,73205598106368000,540340585126398016,5691215305506816000
%N a(n) = phi(9^n+1), where phi is Euler's totient function (A000010).
%H Max Alekseyev, <a href="/A366667/b366667.txt">Table of n, a(n) for n = 0..345</a>
%F a(n) = A000010(A062396(n)). - _Paul F. Marrero Romero_, Nov 04 2023
%F a(n) = A366579(2*n). - _Max Alekseyev_, Jan 08 2024
%t EulerPhi[9^Range[0, 20] + 1] (* _Paul F. Marrero Romero_, Nov 04 2023 *)
%o (PARI) {a(n) = eulerphi(9^n+1)}
%Y Cf. A062396, A000010, A366663, A366664, A366665, A366666.
%Y Cf. A053285, A366579, A366608, A366618, A366630, A366639, A366658, A366669, A366690, A366716.
%K nonn
%O 0,2
%A _Sean A. Irvine_, Oct 15 2023