21987558 has 16 divisors (see below), whose sum is σ = 48861360. Its totient is φ = 7329168.

The previous prime is 21987557. The next prime is 21987571. The reversal of 21987558 is 85578912.

It is a happy number.

21987558 is a `hidden beast` number, since 2 + 1 + 98 + 7 + 558 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987557) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 203535 + ... + 203642.

It is an arithmetic number, because the mean of its divisors is an integer number (3053835).

Almost surely, 2^21987558 is an apocalyptic number.

21987558 is an abundant number, since it is smaller than the sum of its proper divisors (26873802).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21987558 is a wasteful number, since it uses less digits than its factorization.

21987558 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 407188 (or 407182 counting only the distinct ones).

The product of its digits is 201600, while the sum is 45.

The square root of 21987558 is about 4689.0892505901. The cubic root of 21987558 is about 280.1511004176.

The spelling of 21987558 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred fifty-eight".