20808 has 36 divisors (see below), whose sum is σ = 59865.
Its totient is φ = 6528.
The previous prime is 20807. The next prime is 20809. The reversal of 20808 is 80802.
It is a powerful number, because all its prime factors have an exponent greater than 1
and also an Achilles number because it is not a perfect power.
It is an interprime number because it is at equal distance from previous prime (20807) and next prime (20809).
It can be written as a sum of positive squares in 2 ways, for example, as 19044 + 1764 = 138^2 + 42^2
It is a tau number, because it is divible by the number of its divisors (36).
It is an ABA number since it can be written as A⋅BA, here for A=2, B=102.
It is a Harshad number since it is a multiple of its sum of digits (18).
It is a plaindrome in base 7.
It is a zygodrome in base 7.
It is not an unprimeable number, because it can be changed into a prime (20807) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (5) of ones.
It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1216 + ... + 1232.
220808 is an apocalyptic number.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 20808
20808 is an abundant number, since it is smaller than the sum of its proper divisors (39057).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
20808 is a wasteful number, since it uses less digits than its factorization.
20808 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 46 (or 22 counting only the distinct ones).
The product of its (nonzero) digits is 128, while the sum is 18.
The square root of 20808 is about 144.2497833621.
The cubic root of 20808 is about 27.5049027072.
Multiplying 20808 by its sum of digits (18), we get a square (374544 = 6122).
20808 divided by its sum of digits (18) gives a square (1156 = 342).
Multiplying 20808 by its product of nonzero digits (128), we get a square (2663424 = 16322).
Multiplying 20808 by its reverse (80802), we get a square (1681328016 = 410042).
It can be divided in two parts, 20 and 808, that added together give a palindrome (828).
The spelling of 20808 in words is "twenty thousand, eight hundred eight".