21304251 has 24 divisors (see below), whose sum is σ = 31926960. Its totient is φ = 13680576.

The previous prime is 21304237. The next prime is 21304253. The reversal of 21304251 is 15240312.

It is not a de Polignac number, because 21304251 - 2⁵ = 21304219 is a prime.

It is a super-2 number, since 2×21304251² = 907742221342002, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21304253) 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 23 ways as a sum of consecutive naturals, for example, 27765 + ... + 28521.

It is an arithmetic number, because the mean of its divisors is an integer number (1330290).

Almost surely, 2^21304251 is an apocalyptic number.

21304251 is a deficient number, since it is larger than the sum of its proper divisors (10622709).

21304251 is a wasteful number, since it uses less digits than its factorization.

21304251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 875 (or 872 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21304251 is about 4615.6528248992. The cubic root of 21304251 is about 277.2184239049.

Adding to 21304251 its reverse (15240312), we get a palindrome (36544563).

The spelling of 21304251 in words is "twenty-one million, three hundred four thousand, two hundred fifty-one".