Twenty (20) is a positive integer one more than 19 and one less than 21.
20 is an abundant, composite number. Its factorization is 2^2*5. The previous abundant number is 18 and the next is 24.
20, being twice the number base of 10, has sometimes been used as a base for naming numbers.
20 is the fourth tetrahedral number (between 10 and 35).
20 is equal to 10!!!!!!!!, the octuple factorial of 10.
In googology Edit
In Greek-based number-naming systems, 20 is associated with prefix "icosa-", and with prefix "viginti-" in Latin systems.
20 is the base of a googologism by Sbiis Saibian called menger sponge. It is equal to 20^3###^^^###3 in Extended Cascading-E Notation.
Wiki user Denis Maksudov calls this number unalum, and it's equal to f1(10) using the fast-growing hierarchy.
Sbiis Saibian calls the number dekaxis, and it's equal to 10+10 using the addition
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