Repdigit
A 
-repdigit is a number composed of repetition of
a single digit (in a given base, generally taken as base 10 unless otherwise specified).
For example, the beast number 666 is a (base-10)
repdigit. The following table gives the first few repdigits in bases 
to 10.
 | OEIS |  -repdigits |
| 2 | A000225 | 1, 3, 7, 15, 31, 63, 127, ... |
| 3 | A048328 | 1, 2, 4, 8, 13, 26, 40, 80, 121, ... |
| 4 | A048329 | 1, 2, 3, 5, 10, 15, 21, 42, 63, 85, 170, ... |
| 5 | A048330 | 1, 2, 3, 4, 6, 12, 18, 24, 31, 62, 93, 124, 156, ... |
| 6 | A048331 | 1, 2, 3, 4, 5, 7, 14, 21, 28, 35, 43, 86, 129, 172, ... |
| 7 | A048332 | 1, 2, 3, 4, 5, 6, 8, 16, 24, 32, 40, 48, 57, 114, 171, ... |
| 8 | A048333 | 1, 2, 3, 4, 5, 6, 7, 9, 18, 27, 36, 45, 54, 63, 73, 146, ... |
| 9 | A048334 | 1, 2, 3, 4, 5, 6, 7, 8, 10, 20, 30, 40, 50, 60, 70, 80, 91, 182, ... |
| 10 | A010785 | 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, ... |
If the digits of a repdigit are all 1s, it is known as a repunit.
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