- J and K are the only letters not in any of the numbers when written as words.
- Four is the only number that has the same number of letters as its meaning. ( F-O-U-R )
These two fractions add up to one and between them they contain all of the digits from zero to nine. It is the only way that this can be done.
- 18 is the only number that is twice the sum of its digits.
- 40 when written in words " Forty " is the only number with letters in alphabetical order, while One is the only one with letters in reverse order.
- Same Three Digit Number
- Think of any three digit number in which each of the digits is the same. Examples include 333, 666, 777, 999.
- Add up the digits.
- Divide the three digit number by the answer in Step b.
- The answer is 37.
- The decimal fractions of seven are the same six recurring digits, in the same order, but starting from a different one
- 1/7 = 0.142857142857…
2/7 = 0.285714285714…
3/7 = 0.428571428571…
4/7 = 0.571428571428…
5/7 = 0.714285714285…
6/7 = 0.857142857142… - The number Zero does not have its own Roman numeral
- 26 is the only natural number that can be placed between a perfect square and a perfect cube.
Sources : 10 Math Tricks That Will Blow Your Mind
9 Mathematical facts that will blow your mind [and a delicious bonus]