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a(n) = phi(n!+1), where phi is Euler's totient function (A000010).
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%I #12 Oct 21 2023 16:01:12

%S 1,1,2,6,20,110,612,4970,39600,337680,3298900,39916800,442155168,

%T 6151996372,83387930692,1282826630160,19089488332800,355148307803520,

%U 5427568925856000,119931789135468100,2432901890279317572,49902667163053013232,1073067539495604750240

%N a(n) = phi(n!+1), where phi is Euler's totient function (A000010).

%F a(n) = A000010(A038507(n)).

%t EulerPhi[Range[0,25]!+1] (* _Paolo Xausa_, Oct 21 2023 *)

%o (PARI) {a(n) = eulerphi(n!+1)}

%o (Python)

%o from math import factorial

%o from sympy import totient

%o def A366760(n): return totient(factorial(n)+1) # _Chai Wah Wu_, Oct 20 2023

%Y Cf. A038507, A000010, A048855, A366759.

%K nonn

%O 0,3

%A _Sean A. Irvine_, Oct 20 2023