21191855 has 16 divisors (see below), whose sum is σ = 26763264. Its totient is φ = 16077600.

The previous prime is 21191831. The next prime is 21191857. The reversal of 21191855 is 55819112.

It is not a de Polignac number, because 21191855 - 2¹² = 21187759 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21191857) 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, 13880 + ... + 15330.

It is an arithmetic number, because the mean of its divisors is an integer number (1672704).

Almost surely, 2^21191855 is an apocalyptic number.

21191855 is a deficient number, since it is larger than the sum of its proper divisors (5571409).

21191855 is a wasteful number, since it uses less digits than its factorization.

21191855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1606.

The product of its digits is 3600, while the sum is 32.

The square root of 21191855 is about 4603.4611978380. The cubic root of 21191855 is about 276.7300519277.

The spelling of 21191855 in words is "twenty-one million, one hundred ninety-one thousand, eight hundred fifty-five".