21715809 has 8 divisors (see below), whose sum is σ = 29952960. Its totient is φ = 13977936.

The previous prime is 21715807. The next prime is 21715823. The reversal of 21715809 is 90851712.

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

It is not a de Polignac number, because 21715809 - 2¹ = 21715807 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21715809.

It is not an unprimeable number, because it can be changed into a prime (21715807) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 124717 + ... + 124890.

It is an arithmetic number, because the mean of its divisors is an integer number (3744120).

Almost surely, 2^21715809 is an apocalyptic number.

21715809 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21715809 is a deficient number, since it is larger than the sum of its proper divisors (8237151).

21715809 is a wasteful number, since it uses less digits than its factorization.

21715809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 249639.

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21715809 is about 4660.0224248387. The cubic root of 21715809 is about 278.9921632927.

The spelling of 21715809 in words is "twenty-one million, seven hundred fifteen thousand, eight hundred nine".