21878455 has 4 divisors (see below), whose sum is σ = 26254152. Its totient is φ = 17502760.

The previous prime is 21878449. The next prime is 21878459. The reversal of 21878455 is 55487812.

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

It is not a de Polignac number, because 21878455 - 2⁷ = 21878327 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21878459) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2187841 + ... + 2187850.

It is an arithmetic number, because the mean of its divisors is an integer number (6563538).

Almost surely, 2^21878455 is an apocalyptic number.

21878455 is a deficient number, since it is larger than the sum of its proper divisors (4375697).

21878455 is an equidigital number, since it uses as much as digits as its factorization.

21878455 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4375696.

The product of its digits is 89600, while the sum is 40.

The square root of 21878455 is about 4677.4410739207. The cubic root of 21878455 is about 279.6869588225.

The spelling of 21878455 in words is "twenty-one million, eight hundred seventy-eight thousand, four hundred fifty-five".