11.5

Part of 1998 All-Russian Olympiad Regional Round

Problems(1)

7^{1998}. -> 1998^7 - All-Russian MO 1998 Regional (R4) 11.5

Source:

A whole number is written on the board. Its last digit is remembered is then erased and multiplied by

5

added to the number that remained on the board after erasing. The number was originally written

7^{1998}

. After applying several such operations, can one get the number

1998^7

number theoryDigits