21687443 has 4 divisors (see below), whose sum is σ = 21853128. Its totient is φ = 21521760.

The previous prime is 21687373. The next prime is 21687473. The reversal of 21687443 is 34478612.

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

It is a cyclic number.

It is not a de Polignac number, because 21687443 - 2¹⁰ = 21686419 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21687473) by changing a digit.

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, 82646 + ... + 82907.

It is an arithmetic number, because the mean of its divisors is an integer number (5463282).

Almost surely, 2^21687443 is an apocalyptic number.

21687443 is a deficient number, since it is larger than the sum of its proper divisors (165685).

21687443 is a wasteful number, since it uses less digits than its factorization.

21687443 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 165684.

The product of its digits is 32256, while the sum is 35.

The square root of 21687443 is about 4656.9778827046. The cubic root of 21687443 is about 278.8706337039.

The spelling of 21687443 in words is "twenty-one million, six hundred eighty-seven thousand, four hundred forty-three".