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A366922
a(n) is the exponent of 3 in the prime factorization of 10^n - 1.
2
2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 5, 2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 5, 2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 4, 2, 2, 3, 2, 2, 3, 2, 2, 6, 2, 2, 3, 2, 2, 3, 2, 2, 4
OFFSET
1,1
COMMENTS
1
FORMULA
a(n) = A007949(10^n - 1).
a(n) = A007949(n) + 2 = A051064(n) + 1.
MATHEMATICA
a[n_]:=IntegerExponent[10^n-1, 3]; Array[a, 90] (* Stefano Spezia, Oct 28 2023 *)
PROG
(PARI) a366922(n) = valuation(10^n-1, 3)
(Python)
def A366922(n):
c = 0
a, b = divmod(10**n-1, 3)
while b == 0:
a, b = divmod(a, 3)
c += 1
return c # Chai Wah Wu, Oct 29 2023
KEYWORD
nonn,easy
AUTHOR
Hugo Pfoertner, Oct 28 2023
STATUS
approved