A139285 Smallest nontrivial number m that when expressed in base n and then interpreted in base 10, is a multiple of the original number.

3, 2, 7, 6, 5, 308, 51, 34217, 7794416

Offset

1,1

Comments

Not defined for n>9.

Note that for n=1, the unitary numeral system is used, whereas for n>=2, it is the usual base-dependant positional numeral system. - Michel Marcus, Sep 16 2020

Links

Table of n, a(n) for n=1..9.

Example

a(1)=3 since 3 in base 1 ('unary') is 111 and, interpreted in base 10, 111 is a number divisible by 3, whereas 2 in base 1 is 11 and, interpreted in base 10, 11 is not divisible by 2.
a(3)=7 since 7 in base 3 is 21 and, interpreted in base 10, 21 is divisible by 7, whereas 3, 4, 5, 6 in base 3 are, respectively, 10, 11, 12, 20 and, interpreted in base 10, these are numbers not divisible, respectively, by 3, 4, 5, 6.
Trivial solutions (i.e., m<n for n>1 and m=n for n=1) are not considered here.

Prog

(Python)
m, M=2, 11
while M%m>0:
    m, M=m+1, 10*M+1
print(1, m)
for n in range(2, 10):
    m, M, d=n, 10, 10-n
    while M%m>0:
        m=m+1
        u, s=m, 0
        while u%n==0:
            u, s=u//n, 10*s+d
        M=M+1+s
    print(n, m)
# Dimiter Skordev, Sep 28 2020

Crossrefs

Cf. A032551, A032551, A032532.

Sequence in context: A348366 A229120 A255067 * A080398 A126851 A082321

Adjacent sequences: A139282 A139283 A139284 * A139286 A139287 A139288

Keyword

base,fini,full,nonn

Author

Sergio Pimentel, Jun 06 2008

Extensions

a(9) corrected by Giovanni Resta, Nov 02 2017

Status

approved