21909856 has 12 divisors (see below), whose sum is σ = 43135092. Its totient is φ = 10954912.

The previous prime is 21909817. The next prime is 21909857. The reversal of 21909856 is 65890912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21909857) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342310 + ... + 342373.

It is an arithmetic number, because the mean of its divisors is an integer number (3594591).

Almost surely, 2^21909856 is an apocalyptic number.

It is an amenable number.

21909856 is a deficient number, since it is larger than the sum of its proper divisors (21225236).

21909856 is an equidigital number, since it uses as much as digits as its factorization.

21909856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 684693 (or 684685 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21909856 is about 4680.7965134152. The cubic root of 21909856 is about 279.8207015370.

The spelling of 21909856 in words is "twenty-one million, nine hundred nine thousand, eight hundred fifty-six".