From Wikipedia, the free encyclopedia.
Ninety-one (91, XCI) is the natural number following ninety and preceding ninety-two. It is a triangular number, the sum of the squares of the first six integers, as well as a composite number, with its divisors being 7 and 13.
| 91 | |
|---|---|
| Cardinal | ninety-one |
| Ordinal | ninety-first |
| Factorization | |
| Roman numeral | LXXVIII |
| Binary | 1001110 |
| Hexadecimal | 4E |
It is the smallest pseudoprime satisfying the congruence 3n = 3 mod n.
Ninety-one is also:
- The atomic number of protactinium, an actinide.
- The designation of American Interstate 91, a freeway that runs from Connecticut to Vermont.
- The code for international direct dial phone calls to India.
- In cents of a U.S. dollar, the amount of money one has if one has one each of the coins of denominations less than a dollar (penny, nickel, dime, quarter and half dollar).
