21240357 has 4 divisors (see below), whose sum is σ = 28320480. Its totient is φ = 14160236.

The previous prime is 21240313. The next prime is 21240377. The reversal of 21240357 is 75304212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21240357 - 2⁸ = 21240101 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21240377) 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, 3540057 + ... + 3540062.

It is an arithmetic number, because the mean of its divisors is an integer number (7080120).

Almost surely, 2^21240357 is an apocalyptic number.

It is an amenable number.

21240357 is a deficient number, since it is larger than the sum of its proper divisors (7080123).

21240357 is an equidigital number, since it uses as much as digits as its factorization.

21240357 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7080122.

The product of its (nonzero) digits is 1680, while the sum is 24.

The square root of 21240357 is about 4608.7261797594. The cubic root of 21240357 is about 276.9410093029.

Adding to 21240357 its reverse (75304212), we get a palindrome (96544569).

The spelling of 21240357 in words is "twenty-one million, two hundred forty thousand, three hundred fifty-seven".