21856709 has 8 divisors (see below), whose sum is σ = 25260480. Its totient is φ = 18523296.

The previous prime is 21856697. The next prime is 21856733. The reversal of 21856709 is 90765812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21856709 - 2¹⁶ = 21791173 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21856759) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16919 + ... + 18164.

It is an arithmetic number, because the mean of its divisors is an integer number (3157560).

Almost surely, 2^21856709 is an apocalyptic number.

It is an amenable number.

21856709 is a deficient number, since it is larger than the sum of its proper divisors (3403771).

21856709 is an equidigital number, since it uses as much as digits as its factorization.

21856709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35179.

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 21856709 is about 4675.1159343914. The cubic root of 21856709 is about 279.5942635385.

The spelling of 21856709 in words is "twenty-one million, eight hundred fifty-six thousand, seven hundred nine".