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%I #24 Aug 09 2022 09:02:16
%S 1,1,1,2,4,2,1,2,10,6,8,2,4,12,22,12,28,8,20,24,2,24,40,10,2,4,32,52,
%T 2,6,12,48,16,44,36,8,24,2,82,42,88,8,72,2,6,20,48,72,112,36,28,96,8,
%U 4,1,130,66,8,44,24,92,72,32,120,24,78,80,12,172,56,10,178,120,60
%N a(n) = phi(rad(prime(n)-1)), where phi = A000010 and rad = A007947.
%H Michael De Vlieger, <a href="/A356474/b356474.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = Product_{primes p dividing prime(n)-1} (p-1).
%F a(n) = phi(A077063(n)) = A173557(prime(n)-1).
%e prime(8) = 19, so a(8) = phi(rad(18)) = phi(6) = 2.
%t Array[EulerPhi[Times @@ FactorInteger[Prime[#] - 1][[All, 1]]] &, 74] (* _Michael De Vlieger_, Aug 09 2022 *)
%o (PARI) a(n) = my(f=factor(prime(n)-1)[, 1]); prod(k=1, #f, f[k]-1) \\ following _Michel Marcus_'s program for A173557
%Y Cf. A000010, A007947, A077063, A173557.
%K nonn,easy
%O 1,4
%A _Jianing Song_, Aug 09 2022
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