21725815 has 8 divisors (see below), whose sum is σ = 26315280. Its totient is φ = 17217792.

The previous prime is 21725801. The next prime is 21725819. The reversal of 21725815 is 51852712.

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 21725815 - 2⁵ = 21725783 is a prime.

It is a super-2 number, since 2×21725815² = 944022074828450, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21725819) 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, 19770 + ... + 20839.

It is an arithmetic number, because the mean of its divisors is an integer number (3289410).

Almost surely, 2^21725815 is an apocalyptic number.

21725815 is a deficient number, since it is larger than the sum of its proper divisors (4589465).

21725815 is a wasteful number, since it uses less digits than its factorization.

21725815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40721.

The product of its digits is 5600, while the sum is 31.

The square root of 21725815 is about 4661.0959011803. The cubic root of 21725815 is about 279.0350071480.

The spelling of 21725815 in words is "twenty-one million, seven hundred twenty-five thousand, eight hundred fifteen".