Repdigit
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In recreational mathematics, a repdigit is a natural number composed of repeated instances of the same digit, most often in the decimal numeral system.
Examples are 11, 222, 4444, 77777, and 999999. All repdigits are palindromic numbers and are multiples of repunits. One of the most famous repdigits is 666, the number of the beast.
Repdigits are a representation of a number in base x represented by xy − 1 where x and y are natural numbers. For example, the repdigit 77 can be represented as 82 − 1 in base 8 (63 in decimal).
The word repdigit is a portmanteau word, formed from repeated digit.
