21508820 has 12 divisors (see below), whose sum is σ = 45168564. Its totient is φ = 8603520.

The previous prime is 21508801. The next prime is 21508867. The reversal of 21508820 is 2880512.

It can be written as a sum of positive squares in 2 ways, for example, as 3632836 + 17875984 = 1906^2 + 4228^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21508820.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 537701 + ... + 537740.

It is an arithmetic number, because the mean of its divisors is an integer number (3764047).

Almost surely, 2^21508820 is an apocalyptic number.

21508820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21508820 is an abundant number, since it is smaller than the sum of its proper divisors (23659744).

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

21508820 is a wasteful number, since it uses less digits than its factorization.

21508820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1075450 (or 1075448 counting only the distinct ones).

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

The square root of 21508820 is about 4637.7602352860. The cubic root of 21508820 is about 278.1029068845.

The spelling of 21508820 in words is "twenty-one million, five hundred eight thousand, eight hundred twenty".