21540243 has 32 divisors (see below), whose sum is σ = 31852800. Its totient is φ = 12894336.

The previous prime is 21540229. The next prime is 21540247. The reversal of 21540243 is 34204512.

It is not a de Polignac number, because 21540243 - 2⁴ = 21540227 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21540247) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 137121 + ... + 137277.

It is an arithmetic number, because the mean of its divisors is an integer number (995400).

Almost surely, 2^21540243 is an apocalyptic number.

21540243 is a deficient number, since it is larger than the sum of its proper divisors (10312557).

21540243 is a wasteful number, since it uses less digits than its factorization.

21540243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 291.

The product of its (nonzero) digits is 960, while the sum is 21.

The square root of 21540243 is about 4641.1467332977. The cubic root of 21540243 is about 278.2382711285.

Adding to 21540243 its reverse (34204512), we get a palindrome (55744755).

The spelling of 21540243 in words is "twenty-one million, five hundred forty thousand, two hundred forty-three".