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A366821 a(n) is phi(n^n-1) where phi is the Euler totient function.

%I A366821 #25 Jul 04 2024 03:36:18
%S A366821 2,12,128,1400,30240,264992,6635520,141087744,5890320000,114117380608,
%T A366821 4662793175040,99053063903040,5470524984113280,167080949856000000,
%U A366821 9208981628670443520,413582117375670921216,29531731481729468006400,659473218553437863041320
%N A366821 a(n) is phi(n^n-1) where phi is the Euler totient function.
%H A366821 Amiram Eldar, <a href="/A366821/b366821.txt">Table of n, a(n) for n = 2..138</a> (terms 2..102 from Robert G. Wilson v)
%F A366821 a(n) = A000010(A048861(n)).
%p A366821 a:= n-> numtheory[phi](n^n-1):
%p A366821 seq(a(n), n=2..20);  # _Alois P. Heinz_, Oct 26 2023
%t A366821 Array[EulerPhi[#^# - 1] &, 18, 2] (* _Michael De Vlieger_, Oct 24 2023 *)
%o A366821 (PARI) a(n) = eulerphi(n^n-1);
%Y A366821 Cf. A000010, A048861, A064447, A309941, A334167, A344870, A366819, A366822.
%K A366821 nonn
%O A366821 2,1
%A A366821 _Sean A. Irvine_, Oct 24 2023