2 and 5 are the only prime numbers that end in 2 or 5.
It only takes 23 people to enter a room to give you an evens chance that two of them have the same birthday. With 75 people in the room the chances rise to 99 per cent!
If you multiply 111,111,111 × 111,111,111 you get 12,345,678,987,654,321 - a palindrome number that reads the same forwards or backwards. And that works all the way back down to 11 x 11 (121) or just 1 x 1 (1).
Cicadas incubate underground for long periods of time before coming out to mate. Sometimes they spend 13 years underground, sometimes 17. Why? Both those intervals are prime numbers and biologists now believe cicadas adopted those life-cycles to minimize their contact with predators with more round numbered life-cycles.
At sixes and nines, the result of the sum (6 × 9) + (6 + 9) is... 69.
1274953680 has two odd things about it: it uses all the digits 0-9 AND you can divide it exactly by any number from 1-16
10x9x8x7x6x5x4x3x2x1 is the exact number of seconds in six weeks
25% is essentially the same thing as 25/100. Thus taking 25% of 8 is multiplying 25/100 by 8. Since multiplication is commutative 25/1008 is the same thing as 8/10025 which is 8 percent of twenty five.