4

Part of 2005 Finnish National High School Mathematics Competition

Problems(1)

Permuting the digits we obtain an integer divisible by 7

Source: Finnish Mathematics Competition 2005, Final Round, Problem 4

1, 3, 7

9

occur in the decimal representation of an integer. Show that permuting the order of digits one can obtain an integer divisible by

7.

modular arithmeticnumber theory unsolvednumber theory