21987193 has 4 divisors (see below), whose sum is σ = 22523508. Its totient is φ = 21450880.

The previous prime is 21987187. The next prime is 21987197. The reversal of 21987193 is 39178912.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10778089 + 11209104 = 3283^2 + 3348^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21987193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21987197) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 268096 + ... + 268177.

It is an arithmetic number, because the mean of its divisors is an integer number (5630877).

Almost surely, 2^21987193 is an apocalyptic number.

It is an amenable number.

21987193 is a deficient number, since it is larger than the sum of its proper divisors (536315).

21987193 is an equidigital number, since it uses as much as digits as its factorization.

21987193 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 536314.

The product of its digits is 27216, while the sum is 40.

The square root of 21987193 is about 4689.0503302908. The cubic root of 21987193 is about 280.1495502119.

The spelling of 21987193 in words is "twenty-one million, nine hundred eighty-seven thousand, one hundred ninety-three".