- 0 is the additive identity.
- 1 is the multiplicative identity.
- 2 is the only even prime number.
- 3 is the number of spatial dimensions in the world we live in.
- 4 is the smallest number of colours sufficient to colour all planar maps.
- 5 is only prime number which can be expressed as the sum of two consecutive prime numbers.
- 6 is the smallest perfect number.
- 7 is always the sum of numbers on the opposite sides of a dice.
- 8 is the largest cube in the Fibonacci sequence.
- 9 is the maximum number of cubes that are needed to sum any positive integer.
- 10 is the base of our number system.
- 11 is the largest known multiplicative persistence.
- 12 is the smallest abundant number.
- 13 is the number of Archimedean solids.
- 18 is the only positive non-zero number that is twice the sum of its digits.
- 24 is the largest number which is divisible by all numbers less than its square root.
- 25 is the smallest square that can be written as a sum of 2 positive squares.
- 26 is the only positive number which exists between a square and a cube.
- 27 is the largest number that can be represented as the sum of the digits of its cube.
- 28 is the 2nd perfect number after 6.
- 30 is the largest non-zero number, where all the smaller numbers which are relatively prime or co-prime to it are also prime numbers.
- 34 is the smallest non-zero number, which has the same number of divisors as its neighbours have.
- 36 is the 2nd smallest number after one which is both square number and triangular number.
- 40 is the only number when written in letters, the letters appear in alphabetical order. F.O.R.T.Y
- 48 is the smallest number with 10 divisors.
- 50 is the smallest number which can be written as the sum of squares of two non-zero numbers in two different ways.
