21457123 has 4 divisors (see below), whose sum is σ = 21759408. Its totient is φ = 21154840.

The previous prime is 21457087. The next prime is 21457133. The reversal of 21457123 is 32175412.

It is a happy number.

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-21457123 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21457133) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 151036 + ... + 151177.

It is an arithmetic number, because the mean of its divisors is an integer number (5439852).

Almost surely, 2^21457123 is an apocalyptic number.

21457123 is a deficient number, since it is larger than the sum of its proper divisors (302285).

21457123 is an equidigital number, since it uses as much as digits as its factorization.

21457123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 302284.

The product of its digits is 1680, while the sum is 25.

The square root of 21457123 is about 4632.1833944696. The cubic root of 21457123 is about 277.8799189824.

The spelling of 21457123 in words is "twenty-one million, four hundred fifty-seven thousand, one hundred twenty-three".