21805949 has 16 divisors (see below), whose sum is σ = 24525504. Its totient is φ = 19219200.

The previous prime is 21805943. The next prime is 21805963. The reversal of 21805949 is 94950812.

It is not a de Polignac number, because 21805949 - 2⁴ = 21805933 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805943) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 65714 + ... + 66044.

It is an arithmetic number, because the mean of its divisors is an integer number (1532844).

Almost surely, 2^21805949 is an apocalyptic number.

It is an amenable number.

21805949 is a deficient number, since it is larger than the sum of its proper divisors (2719555).

21805949 is a wasteful number, since it uses less digits than its factorization.

21805949 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 508.

The product of its (nonzero) digits is 25920, while the sum is 38.

The square root of 21805949 is about 4669.6840364205. The cubic root of 21805949 is about 279.3776526164.

The spelling of 21805949 in words is "twenty-one million, eight hundred five thousand, nine hundred forty-nine".