Repdigit

In recreational mathematics, a repdigit or sometimes monodigit is a natural number composed of repeated instances of the same digit in a positional number system (often implicitly decimal).

The word is a portmanteau of "repeated" and "digit". Examples are 11, 666, 4444, and 999999.

All repdigits are palindromic numbers and are multiples of repunits.

Other well-known repdigits include the repunit primes and in particular the Mersenne primes (which are repdigits when represented in binary).

The concept of a repdigit has been studied under that name since at least 1974,[5] and earlier Beiler (1966) called them "monodigit numbers".

As of 2023, a number of popular media publications have published articles suggesting that repunit numbers have numerological significance, describing them as "angel numbers".

Look it up on Wikipedia 

Photo: Pixabay/chenspec

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