21857881 has 4 divisors (see below), whose sum is σ = 21889764. Its totient is φ = 21826000.

The previous prime is 21857873. The next prime is 21857887. The reversal of 21857881 is 18875812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8462281 + 13395600 = 2909^2 + 3660^2 .

It is a cyclic number.

It is not a de Polignac number, because 21857881 - 2³ = 21857873 is a prime.

It is a super-2 number, since 2×21857881² = 955533923620322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21857887) 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, 14890 + ... + 16291.

It is an arithmetic number, because the mean of its divisors is an integer number (5472441).

Almost surely, 2^21857881 is an apocalyptic number.

It is an amenable number.

21857881 is a deficient number, since it is larger than the sum of its proper divisors (31883).

21857881 is an equidigital number, since it uses as much as digits as its factorization.

21857881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31882.

The product of its digits is 35840, while the sum is 40.

The square root of 21857881 is about 4675.2412771963. The cubic root of 21857881 is about 279.5992609151.

The spelling of 21857881 in words is "twenty-one million, eight hundred fifty-seven thousand, eight hundred eighty-one".