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 .
The word repdigit is a portmanteau word, formed from repeated digit .