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a(n) = phi(11^n-1), where phi is Euler's totient function (A000010).
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%I #9 Jan 04 2024 19:14:41

%S 4,32,432,3840,64400,373248,7613424,56217600,765889344,6913984000,

%T 114117380608,599824465920,13796450740800,98909341090560,

%U 1356399209088000,11341872916070400,202178811399717504,1171410130065973248,24463636179365818512,176391086415667200000

%N a(n) = phi(11^n-1), where phi is Euler's totient function (A000010).

%H Max Alekseyev, <a href="/A366685/b366685.txt">Table of n, a(n) for n = 1..316</a>

%t EulerPhi[11^Range[30] - 1]

%o (PARI) {a(n) = eulerphi(11^n-1)}

%Y 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), A366663 (k=9), A295503 (k=10), this sequence (k=11), A366711 (k=12).

%Y Cf. A000010, A024127, A366681, A366682, A366683, A366684.

%K nonn

%O 1,1

%A _Sean A. Irvine_, Oct 16 2023