21805881 has 8 divisors (see below), whose sum is σ = 29179104. Its totient is φ = 14484960.

The previous prime is 21805877. The next prime is 21805907. The reversal of 21805881 is 18850812.

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

It is not a de Polignac number, because 21805881 - 2² = 21805877 is a prime.

It is a super-2 number, since 2×21805881² = 950992892372322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21805811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12091 + ... + 13776.

It is an arithmetic number, because the mean of its divisors is an integer number (3647388).

Almost surely, 2^21805881 is an apocalyptic number.

It is an amenable number.

21805881 is a deficient number, since it is larger than the sum of its proper divisors (7373223).

21805881 is a wasteful number, since it uses less digits than its factorization.

21805881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26151.

The product of its (nonzero) digits is 5120, while the sum is 33.

The square root of 21805881 is about 4669.6767554082. The cubic root of 21805881 is about 279.3773622110.

The spelling of 21805881 in words is "twenty-one million, eight hundred five thousand, eight hundred eighty-one".