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

Author

Hugo Pfoertner, Oct 28 2023

Keywords

• nonn
• easy

Comments

1

Crossrefs

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

Programs

Mathematica

a[n_]:=IntegerExponent[10^n-1,3]; Array[a,90] (* Stefano Spezia, Oct 28 2023 *)

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

Formula

a(n) = A007949(10^n - 1).

a(n) = A007949(n) + 2 = A051064(n) + 1.