21543391 has 4 divisors (see below), whose sum is σ = 21713152. Its totient is φ = 21373632.

The previous prime is 21543373. The next prime is 21543407. The reversal of 21543391 is 19334512.

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 21543391 - 2⁹ = 21542879 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 (21543331) 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, 84690 + ... + 84943.

It is an arithmetic number, because the mean of its divisors is an integer number (5428288).

Almost surely, 2^21543391 is an apocalyptic number.

21543391 is a deficient number, since it is larger than the sum of its proper divisors (169761).

21543391 is a wasteful number, since it uses less digits than its factorization.

21543391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 169760.

The product of its digits is 3240, while the sum is 28.

The square root of 21543391 is about 4641.4858612302. The cubic root of 21543391 is about 278.2518248507.

The spelling of 21543391 in words is "twenty-one million, five hundred forty-three thousand, three hundred ninety-one".