21931249 has 4 divisors (see below), whose sum is σ = 22104064. Its totient is φ = 21758436.

The previous prime is 21931243. The next prime is 21931253. The reversal of 21931249 is 94213912.

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 21931249 - 2⁹ = 21930737 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21931249.

It is not an unprimeable number, because it can be changed into a prime (21931243) 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, 86217 + ... + 86470.

It is an arithmetic number, because the mean of its divisors is an integer number (5526016).

Almost surely, 2^21931249 is an apocalyptic number.

It is an amenable number.

21931249 is a deficient number, since it is larger than the sum of its proper divisors (172815).

21931249 is a wasteful number, since it uses less digits than its factorization.

21931249 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 172814.

The product of its digits is 3888, while the sum is 31.

The square root of 21931249 is about 4683.0811438624. The cubic root of 21931249 is about 279.9117451445.

The spelling of 21931249 in words is "twenty-one million, nine hundred thirty-one thousand, two hundred forty-nine".