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A366760
a(n) = phi(n!+1), where phi is Euler's totient function (A000010).
2
1, 1, 2, 6, 20, 110, 612, 4970, 39600, 337680, 3298900, 39916800, 442155168, 6151996372, 83387930692, 1282826630160, 19089488332800, 355148307803520, 5427568925856000, 119931789135468100, 2432901890279317572, 49902667163053013232, 1073067539495604750240
OFFSET
0,3
FORMULA
a(n) = A000010(A038507(n)).
MATHEMATICA
EulerPhi[Range[0, 25]!+1] (* Paolo Xausa, Oct 21 2023 *)
PROG
(PARI) {a(n) = eulerphi(n!+1)}
(Python)
from math import factorial
from sympy import totient
def A366760(n): return totient(factorial(n)+1) # Chai Wah Wu, Oct 20 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 20 2023
STATUS
approved