31 (thirty-one) is a positive integer following 30 and preceding 32. Its ordinal form is written "thirty-first" or "31st".

Properties Edit

31 is an odd prime number. It is a Mersenne prime, since it is equal to 2^5-1.

31 is a primorial prime.

31 is the largest number whose square contains all digits in descending order.

Pi-related stuff Edit

The integral parts of π3, 10π and 3π are all equal to 31.

The number π3 is almost equal to 31. The emphasis is on “almost”, since π is a transcendental number.

In googology Edit

In Greek-based number-naming systems, 31 is associated with prefix "hentriaconta-", and with prefix "untriginti-" in Latin systems.