21805240 has 16 divisors (see below), whose sum is σ = 49061880. Its totient is φ = 8722080.

The previous prime is 21805229. The next prime is 21805283. The reversal of 21805240 is 4250812.

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, 272526 + ... + 272605.

Almost surely, 2^21805240 is an apocalyptic number.

21805240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21805240 is an abundant number, since it is smaller than the sum of its proper divisors (27256640).

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

21805240 is a wasteful number, since it uses less digits than its factorization.

21805240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 545142 (or 545138 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 22.

The square root of 21805240 is about 4669.6081206028. The cubic root of 21805240 is about 279.3746246827.

The spelling of 21805240 in words is "twenty-one million, eight hundred five thousand, two hundred forty".