21808528 has 30 divisors (see below), whose sum is σ = 49154406. Its totient is φ = 9346176.

The previous prime is 21808519. The next prime is 21808529. The reversal of 21808528 is 82580812.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 19079424 + 2729104 = 4368^2 + 1652^2 .

It is a super-2 number, since 2×21808528² = 951223787053568, which contains 22 as substring.

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 21808493 and 21808502.

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 5 ways as a sum of consecutive naturals, for example, 13125 + ... + 14692.

Almost surely, 2^21808528 is an apocalyptic number.

21808528 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21808528 is an abundant number, since it is smaller than the sum of its proper divisors (27345878).

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

21808528 is a wasteful number, since it uses less digits than its factorization.

21808528 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27839 (or 27826 counting only the distinct ones).

The product of its (nonzero) digits is 10240, while the sum is 34.

The square root of 21808528 is about 4669.9601711364. The cubic root of 21808528 is about 279.3886662250.

The spelling of 21808528 in words is "twenty-one million, eight hundred eight thousand, five hundred twenty-eight".