21878857 has 24 divisors (see below), whose sum is σ = 29613248. Its totient is φ = 15729120.

The previous prime is 21878849. The next prime is 21878867. The reversal of 21878857 is 75887812.

It is a happy number.

It is not a de Polignac number, because 21878857 - 2³ = 21878849 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21878827) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 10018 + ... + 12004.

Almost surely, 2^21878857 is an apocalyptic number.

It is an amenable number.

21878857 is a deficient number, since it is larger than the sum of its proper divisors (7734391).

21878857 is a wasteful number, since it uses less digits than its factorization.

21878857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2029 (or 2018 counting only the distinct ones).

The product of its digits is 250880, while the sum is 46.

The square root of 21878857 is about 4677.4840459375. The cubic root of 21878857 is about 279.6886718239.

It can be divided in two parts, 21 and 878857, that added together give a palindrome (878878).

The spelling of 21878857 in words is "twenty-one million, eight hundred seventy-eight thousand, eight hundred fifty-seven".