What are some interesting facts about the number 21?
and that is my fav number =]
21 is the fifth discrete bi-prime and the second in the (3.q) family. With 22 it forms the second discrete bi-prime pair. 21 has an aliquot sum of 11 though it is the second composite number found in the 11-aliquot tree with. 18 is the first such member as well having as 21 as its aliquot sum 21 is the first number to be the aliquot sum of three numbers 18,51,91
21 appears in the Padovan sequence, preceded by the terms 9, 12, 16 (it is the sum of the first two of these).
The sum of divisors for the integers 1 through 5 is 21.
21 is a repdigit in base 4 (111).
21 is the smallest number of differently sized squares needed to square the square.
It is a proper number.
It is the minimum drinking age in many countries, notably the US.
2 ) Drinking age in most states
3 ) You can gamble
4 ) Cows graze in the wild in groups of an average of 21 cows
2) Age of complete adulthood in the US
3) Counting, backward (instead of 1,2= 12)
and legal drinking age :]
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