MathDB

We want to choose telephone numbers for a city. The numbers have

10

digits and

0

isn’t used in the numbers. Our aim is: We don’t choose some numbers such that every

2

telephone numbers are different in more than one digit OR every

2

telephone numbers are different in a digit which is more than

1

. What is the maximum number of telephone numbers which can be chosen? In how many ways, can we choose the numbers in this maximum situation?

Problem Statement