MathDB
10digit, position in decimal representation equal to no of digits in number

Source: Lusophon 2015 CPLP P2

August 29, 2018
number theoryDigitDigitsdecimal representation

Problem Statement

Determine all ten-digit numbers whose decimal a0a1a2a3a4a5a6a7a8a9\overline{a_0a_1a_2a_3a_4a_5a_6a_7a_8a_9} is given by such that for each integer jj with 0j9,aj0\le j \le 9, a_j is equal to the number of digits equal to jj in this representation. That is: the first digit is equal to the amount of "00" in the writing of that number, the second digit is equal to the amount of "11" in the writing of that number, the third digit is equal to the amount of "22" in the writing of that number, ... , the tenth digit is equal to the number of "99" in the writing of that number.