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Number theory Difficulty 6.3 National olympiad Find the answer

Is there an eight-digit number without zero digits, which when divided by the first digit gives the remainder 11, when divided by the second digit will give the remainder 22, ..., when divided by the eighth digit will give the remainder 88?

A number or a short expression. Spacing and $ signs are ignored.

Solution

We are tasked with determining if there exists an eight-digit number, where none of its digits is zero, that satisfies the following conditions:

1. When the number is divided by its first digit, the remainder is 1.
2. When the number is divided by its second digit, the remainder is 2.
3. When the number is divided by its third digit, the remainder is 3.
4. When the number is divided by its fourth digit, the remainder is 4.
5. When the number is divided by its fifth digit, the remainder is 5.
6. When the number is divided by its sixth digit, the remainder is 6.
7. When the number is divided by its seventh digit, the remainder is 7.
8. When the number is divided by its eighth digit, the remainder is 8.

Let's denote the eight-digit number by N N , and its digits by a1,a2,,a8 a_1, a_2, \ldots, a_8 such that N=a1a2a8 N = \overline{a_1 a_2 \cdots a_8} .

Given the conditions:
- N1(moda1) N \equiv 1 \pmod{a_1}
- N2(moda2) N \equiv 2 \pmod{a_2}
- N3(moda3) N \equiv 3 \pmod{a_3}
- N4(moda4) N \equiv 4 \pmod{a_4}
- N5(moda5) N \equiv 5 \pmod{a_5}
- N6(moda6) N \equiv 6 \pmod{a_6}
- N7(moda7) N \equiv 7 \pmod{a_7}
- N8(moda8) N \equiv 8 \pmod{a_8}

Analyzing these requirements, each ai a_i must be greater than the constant residues, namely a1>1 a_1 > 1 , a2>2 a_2 > 2 , a3>3 a_3 > 3 , \ldots , a8>8 a_8 > 8 .

Because a1,a2,,a8 a_1, a_2, \ldots, a_8 are each digits (from 1 to 9), the condition a8>8 a_8 > 8 implies that a8 a_8 must be greater than 8. However, since digits can only be from 1 to 9, the only possible value for a8 a_8 would then be 9. But a99 a_9 \neq 9 since a9>9 a_9 > 9 is not a digit.

This contradiction indicates that no such eight-digit number exists because it is not possible to satisfy all of the conditions with digits from 1 to 9. Thus:

No such number exists \boxed{\text{No such number exists}}

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Source: Omni-MATH, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.