A366922 a(n) is the exponent of 3 in the prime factorization of 10^n - 1.

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

Links

Table of n, a(n) for n=1..90.

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

Crossrefs

Cf. A002283, A003020, A007949, A051064, A057951, A102347, A366921.

Sequence in context: A082204 A152727 A087159 * A218800 A062502 A141242

Adjacent sequences: A366919 A366920 A366921 * A366923 A366924 A366925

Keyword

nonn,easy

Author

Hugo Pfoertner, Oct 28 2023

Status

approved