A356474 a(n) = phi(rad(prime(n)-1)), where phi = A000010 and rad = A007947.

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, 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, 4, 1, 130, 66, 8, 44, 24, 92, 72, 32, 120, 24, 78, 80, 12, 172, 56, 10, 178, 120, 60

Offset: 1

Author

Jianing Song, Aug 09 2022

Keywords

• nonn
• easy

Examples

			prime(8) = 19, so a(8) = phi(rad(18)) = phi(6) = 2.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A007947, A077063, A173557.

Programs

Mathematica

Array[EulerPhi[Times @@ FactorInteger[Prime[#] - 1][[All, 1]]] &, 74] (* Michael De Vlieger, Aug 09 2022 *)

PARI

a(n) = my(f=factor(prime(n)-1)[, 1]); prod(k=1, #f, f[k]-1) \\ following Michel Marcus's program for A173557

Formula

a(n) = Product_{primes p dividing prime(n)-1} (p-1).

a(n) = phi(A077063(n)) = A173557(prime(n)-1).