21238251 has 4 divisors (see below), whose sum is σ = 28317672. Its totient is φ = 14158832.

The previous prime is 21238249. The next prime is 21238271. The reversal of 21238251 is 15283212.

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

It is a cyclic number.

It is not a de Polignac number, because 21238251 - 2¹ = 21238249 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21238211) 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, 3539706 + ... + 3539711.

It is an arithmetic number, because the mean of its divisors is an integer number (7079418).

Almost surely, 2^21238251 is an apocalyptic number.

21238251 is a deficient number, since it is larger than the sum of its proper divisors (7079421).

21238251 is an equidigital number, since it uses as much as digits as its factorization.

21238251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7079420.

The product of its digits is 960, while the sum is 24.

The square root of 21238251 is about 4608.4976944770. The cubic root of 21238251 is about 276.9318560192.

The spelling of 21238251 in words is "twenty-one million, two hundred thirty-eight thousand, two hundred fifty-one".