21705500 has 24 divisors (see below), whose sum is σ = 47405904. Its totient is φ = 8682000.

The previous prime is 21705479. The next prime is 21705503. The reversal of 21705500 is 550712.

It is a super-2 number, since 2×21705500² = 942257460500000, which contains 22 as substring.

It is a hoax number, since the sum of its digits (20) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705503) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21206 + ... + 22205.

It is an arithmetic number, because the mean of its divisors is an integer number (1975246).

Almost surely, 2^21705500 is an apocalyptic number.

21705500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21705500 is an abundant number, since it is smaller than the sum of its proper divisors (25700404).

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

21705500 is a wasteful number, since it uses less digits than its factorization.

21705500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43430 (or 43418 counting only the distinct ones).

The product of its (nonzero) digits is 350, while the sum is 20.

The square root of 21705500 is about 4658.9161829765. The cubic root of 21705500 is about 278.9480082802.

The spelling of 21705500 in words is "twenty-one million, seven hundred five thousand, five hundred".