21239749 has 4 divisors (see below), whose sum is σ = 22489164. Its totient is φ = 19990336.

The previous prime is 21239731. The next prime is 21239753. The reversal of 21239749 is 94793212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 14516100 + 6723649 = 3810^2 + 2593^2 .

It is a cyclic number.

It is not a de Polignac number, because 21239749 - 2⁵ = 21239717 is a prime.

It is a super-2 number, since 2×21239749² = 902253875166002, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21239759) 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, 624682 + ... + 624715.

It is an arithmetic number, because the mean of its divisors is an integer number (5622291).

Almost surely, 2^21239749 is an apocalyptic number.

It is an amenable number.

21239749 is a deficient number, since it is larger than the sum of its proper divisors (1249415).

21239749 is a wasteful number, since it uses less digits than its factorization.

21239749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1249414.

The product of its digits is 27216, while the sum is 37.

The square root of 21239749 is about 4608.6602174602. The cubic root of 21239749 is about 276.9383668216.

The spelling of 21239749 in words is "twenty-one million, two hundred thirty-nine thousand, seven hundred forty-nine".