A018870 9^a(n) is smallest power of 9 beginning with n.

0, 12, 9, 7, 5, 4, 3, 2, 1, 21, 42, 20, 19, 40, 18, 17, 60, 16, 59, 15, 80, 14, 101, 57, 13, 78, 34, 12, 77, 33, 11, 98, 54, 10, 119, 75, 53, 9, 118, 96, 52, 30, 8, 95, 73, 51, 7, 138, 94, 72, 50, 28, 6, 115, 93, 71, 49, 27, 5, 114, 92, 70, 48, 26, 4, 135, 113, 91, 69, 47, 25, 3, 134

Offset

1,2

Links

D. Mondot, Table of n, a(n) for n = 1..32699

Example

a(2) = 12 since 9^12 = 282429536481 is the smallest power of 9 that begins with 2.

Prog

(Python)
def a(n):
    s, k = str(n), 0
    while not str(9**k).startswith(s): k += 1
    return k
print([a(n) for n in range(1, 74)]) # Michael S. Branicky, Dec 09 2021

Crossrefs

Cf. A001019, A018869.

Sequence in context: A299515 A326927 A338289 * A327470 A068614 A163920

Adjacent sequences: A018867 A018868 A018869 * A018871 A018872 A018873

Keyword

nonn,base

Author

David W. Wilson

Status

approved