21987387 has 12 divisors (see below), whose sum is σ = 31951920. Its totient is φ = 14569488.

The previous prime is 21987373. The next prime is 21987403. The reversal of 21987387 is 78378912.

It is not a de Polignac number, because 21987387 - 2²⁰ = 20938811 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21987187) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5812 + ... + 8817.

It is an arithmetic number, because the mean of its divisors is an integer number (2662660).

Almost surely, 2^21987387 is an apocalyptic number.

21987387 is a deficient number, since it is larger than the sum of its proper divisors (9964533).

21987387 is a wasteful number, since it uses less digits than its factorization.

21987387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14802 (or 14799 counting only the distinct ones).

The product of its digits is 169344, while the sum is 45.

The square root of 21987387 is about 4689.0710167367. The cubic root of 21987387 is about 280.1503741590.

The spelling of 21987387 in words is "twenty-one million, nine hundred eighty-seven thousand, three hundred eighty-seven".