| No. of known terms | 11 |
|---|---|
| Conjectured no. of terms | Infinite |
| First terms | 11, 1111111111111111111, 11111111111111111111111 |
| Largest known term | (108177207−1)/9 |
| OEIS index |
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In recreational mathematics, a repunit is a number like 11, 111, or 1111 that contains only the digit 1 — a more specific type of repdigit. The term stands for "repeated unit" and was coined in 1966 by Albert H. Beiler in his book Recreations in the Theory of Numbers.[note 1]
A repunit prime is a repunit that is also a prime number. Primes that are repunits in base-2 are Mersenne primes. As of October 2024, the largest known prime number 2136,279,841 − 1, the largest probable prime R8177207 and the largest elliptic curve primality-proven prime R86453 are all repunits in various bases.
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