21808520 has 16 divisors (see below), whose sum is σ = 49069260. Its totient is φ = 8723392.

The previous prime is 21808519. The next prime is 21808529. The reversal of 21808520 is 2580812.

It can be written as a sum of positive squares in 2 ways, for example, as 21696964 + 111556 = 4658^2 + 334^2 .

It is a super-2 number, since 2×21808520² = 951223089180800, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21808520.

It is not an unprimeable number, because it can be changed into a prime (21808529) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 272567 + ... + 272646.

Almost surely, 2^21808520 is an apocalyptic number.

21808520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21808520 is an abundant number, since it is smaller than the sum of its proper divisors (27260740).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21808520 is a wasteful number, since it uses less digits than its factorization.

21808520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 545224 (or 545220 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 26.

The square root of 21808520 is about 4669.9593145979. The cubic root of 21808520 is about 279.3886320624.

The spelling of 21808520 in words is "twenty-one million, eight hundred eight thousand, five hundred twenty".