MathDB
Common Sequences

Source: Malaysian SST 2024 P2

September 5, 2024
number theoryDigits

Problem Statement

A finite sequence of decimal digits from {0,1,,9}\{0,1,\cdots, 9\} is said to be common if for each sufficiently large positive integer nn, there exists a positive integer mm such that the expansion of nn in base mm ends with this sequence of digits.
For example, 00 is common because for any large nn, the expansion of nn in base nn is 1010, whereas 0000 is not common because for any squarefree nn, the expansion of nn in any base cannot end with 0000.
Determine all common sequences.
Proposed by Wong Jer Ren