21987287 has 16 divisors (see below), whose sum is σ = 26936832. Its totient is φ = 17534880.

The previous prime is 21987269. The next prime is 21987293. The reversal of 21987287 is 78278912.

It is a cyclic number.

It is not a de Polignac number, because 21987287 - 2⁶ = 21987223 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 (21987247) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4112 + ... + 7802.

It is an arithmetic number, because the mean of its divisors is an integer number (1683552).

Almost surely, 2^21987287 is an apocalyptic number.

21987287 is a deficient number, since it is larger than the sum of its proper divisors (4949545).

21987287 is a wasteful number, since it uses less digits than its factorization.

21987287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3758.

The product of its digits is 112896, while the sum is 44.

The square root of 21987287 is about 4689.0603536316. The cubic root of 21987287 is about 280.1499494446.

The spelling of 21987287 in words is "twenty-one million, nine hundred eighty-seven thousand, two hundred eighty-seven".