21856643 has 4 divisors (see below), whose sum is σ = 22561728. Its totient is φ = 21151560.

The previous prime is 21856621. The next prime is 21856657. The reversal of 21856643 is 34665812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21856643 - 2⁶ = 21856579 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21856613) 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, 352496 + ... + 352557.

It is an arithmetic number, because the mean of its divisors is an integer number (5640432).

Almost surely, 2^21856643 is an apocalyptic number.

21856643 is a deficient number, since it is larger than the sum of its proper divisors (705085).

21856643 is an equidigital number, since it uses as much as digits as its factorization.

21856643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 705084.

The product of its digits is 34560, while the sum is 35.

The square root of 21856643 is about 4675.1088757375. The cubic root of 21856643 is about 279.5939821109.

The spelling of 21856643 in words is "twenty-one million, eight hundred fifty-six thousand, six hundred forty-three".