21087188 has 24 divisors (see below), whose sum is σ = 39900000. Its totient is φ = 9717408.

The previous prime is 21087173. The next prime is 21087193. The reversal of 21087188 is 88178012.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 938 + ... + 6561.

It is an arithmetic number, because the mean of its divisors is an integer number (1662500).

Almost surely, 2^21087188 is an apocalyptic number.

It is an amenable number.

21087188 is a deficient number, since it is larger than the sum of its proper divisors (18812812).

21087188 is a wasteful number, since it uses less digits than its factorization.

21087188 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7559 (or 7557 counting only the distinct ones).

The product of its (nonzero) digits is 7168, while the sum is 35.

The square root of 21087188 is about 4592.0788320759. The cubic root of 21087188 is about 276.2737080313.

The spelling of 21087188 in words is "twenty-one million, eighty-seven thousand, one hundred eighty-eight".