21207457 has 4 divisors (see below), whose sum is σ = 21216816. Its totient is φ = 21198100.

The previous prime is 21207437. The next prime is 21207467. The reversal of 21207457 is 75470212.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21207457 - 2²³ = 12818849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21207437) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1098 + ... + 6604.

It is an arithmetic number, because the mean of its divisors is an integer number (5304204).

Almost surely, 2^21207457 is an apocalyptic number.

It is an amenable number.

21207457 is a deficient number, since it is larger than the sum of its proper divisors (9359).

21207457 is an equidigital number, since it uses as much as digits as its factorization.

21207457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9358.

The product of its (nonzero) digits is 3920, while the sum is 28.

The square root of 21207457 is about 4605.1554805457. The cubic root of 21207457 is about 276.7979472447.

Adding to 21207457 its reverse (75470212), we get a palindrome (96677669).

The spelling of 21207457 in words is "twenty-one million, two hundred seven thousand, four hundred fifty-seven".