21040243 has 4 divisors (see below), whose sum is σ = 24046000. Its totient is φ = 18034488.

The previous prime is 21040231. The next prime is 21040247. The reversal of 21040243 is 34204012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21040243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21040247) 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, 1502868 + ... + 1502881.

It is an arithmetic number, because the mean of its divisors is an integer number (6011500).

Almost surely, 2^21040243 is an apocalyptic number.

21040243 is a deficient number, since it is larger than the sum of its proper divisors (3005757).

21040243 is an equidigital number, since it uses as much as digits as its factorization.

21040243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3005756.

The product of its (nonzero) digits is 192, while the sum is 16.

The square root of 21040243 is about 4586.9644646542. The cubic root of 21040243 is about 276.0685391289.

Adding to 21040243 its reverse (34204012), we get a palindrome (55244255).

The spelling of 21040243 in words is "twenty-one million, forty thousand, two hundred forty-three".