21864815 has 8 divisors (see below), whose sum is σ = 29986080. Its totient is φ = 14992992.

The previous prime is 21864797. The next prime is 21864853. The reversal of 21864815 is 51846812.

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

It is not a de Polignac number, because 21864815 - 2¹⁶ = 21799279 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35), and also a Moran number because the ratio is a prime number: 624709 = 21864815 / (2 + 1 + 8 + 6 + 4 + 8 + 1 + 5).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 312320 + ... + 312389.

It is an arithmetic number, because the mean of its divisors is an integer number (3748260).

Almost surely, 2^21864815 is an apocalyptic number.

21864815 is a deficient number, since it is larger than the sum of its proper divisors (8121265).

21864815 is an equidigital number, since it uses as much as digits as its factorization.

21864815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 624721.

The product of its digits is 15360, while the sum is 35.

The square root of 21864815 is about 4675.9827843994. The cubic root of 21864815 is about 279.6288236512.

The spelling of 21864815 in words is "twenty-one million, eight hundred sixty-four thousand, eight hundred fifteen".