21987566 has 8 divisors (see below), whose sum is σ = 33030504. Its totient is φ = 10977400.

The previous prime is 21987557. The next prime is 21987571. The reversal of 21987566 is 66578912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6440 + ... + 9243.

It is an arithmetic number, because the mean of its divisors is an integer number (4128813).

Almost surely, 2^21987566 is an apocalyptic number.

21987566 is a deficient number, since it is larger than the sum of its proper divisors (11042938).

21987566 is a wasteful number, since it uses less digits than its factorization.

21987566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16386.

The product of its digits is 181440, while the sum is 44.

The square root of 21987566 is about 4689.0901036342. The cubic root of 21987566 is about 280.1511343946.

The spelling of 21987566 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred sixty-six".