21917855 has 4 divisors (see below), whose sum is σ = 26301432. Its totient is φ = 17534280.

The previous prime is 21917843. The next prime is 21917867. The reversal of 21917855 is 55871912.

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

It is an interprime number because it is at equal distance from previous prime (21917843) and next prime (21917867).

It is not a de Polignac number, because 21917855 - 2²⁰ = 20869279 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2191781 + ... + 2191790.

It is an arithmetic number, because the mean of its divisors is an integer number (6575358).

Almost surely, 2^21917855 is an apocalyptic number.

21917855 is a deficient number, since it is larger than the sum of its proper divisors (4383577).

21917855 is an equidigital number, since it uses as much as digits as its factorization.

21917855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4383576.

The product of its digits is 25200, while the sum is 38.

The square root of 21917855 is about 4681.6508840365. The cubic root of 21917855 is about 279.8547503452.

The spelling of 21917855 in words is "twenty-one million, nine hundred seventeen thousand, eight hundred fifty-five".