21909855 has 64 divisors (see below), whose sum is σ = 41430528. Its totient is φ = 9768960.

The previous prime is 21909817. The next prime is 21909857. The reversal of 21909855 is 55890912.

It is not a de Polignac number, because 21909855 - 2¹⁵ = 21877087 is a prime.

It is a super-2 number, since 2×21909855² = 960083492242050, which contains 22 as substring.

21909855 is a modest number, since divided by 9855 gives 2190 as remainder.

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 in 63 ways as a sum of consecutive naturals, for example, 204712 + ... + 204818.

It is an arithmetic number, because the mean of its divisors is an integer number (647352).

Almost surely, 2^21909855 is an apocalyptic number.

21909855 is a deficient number, since it is larger than the sum of its proper divisors (19520673).

21909855 is a wasteful number, since it uses less digits than its factorization.

21909855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216.

The product of its (nonzero) digits is 32400, while the sum is 39.

The square root of 21909855 is about 4680.7964065958. The cubic root of 21909855 is about 279.8206972798.

The spelling of 21909855 in words is "twenty-one million, nine hundred nine thousand, eight hundred fifty-five".