2

Part of 1955 Poland - Second Round

Problems(1)

1 + 2 + 3 + .. + n = three-digit number with identical digits.

Source: Polish MO second round 1955 p2

Find the natural number

n

knowing that the sum

1 + 2 + 3 + \ldots + n

is a three-digit number with identical digits.

number theoryDigits