| 1 | For example, the year 2000 was a leap year, but the year 1900 was not, because when divided by 400, it does not render a whole number. | |
| 2 | The integer 1 is divisible only by itself; it is not a prime. | |
| 3 | The number 17, for example, is prime, because it is divisible only by 1 and 17. | |
| 4 | Years that are divisible by 100 are not leap years, unless they're also divisible by 400. | |
| 5 | JANE STREET CAPITAL: "What is the smallest number divisible by 225 that consists of all 1s and 0s?" |