21243724 has 6 divisors (see below), whose sum is σ = 37176524. Its totient is φ = 10621860.

The previous prime is 21243721. The next prime is 21243731. The reversal of 21243724 is 42734212.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21243721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2655462 + ... + 2655469.

Almost surely, 2^21243724 is an apocalyptic number.

It is an amenable number.

21243724 is a deficient number, since it is larger than the sum of its proper divisors (15932800).

21243724 is a wasteful number, since it uses less digits than its factorization.

21243724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5310935 (or 5310933 counting only the distinct ones).

The product of its digits is 2688, while the sum is 25.

The square root of 21243724 is about 4609.0914506006. The cubic root of 21243724 is about 276.9556419997.

Adding to 21243724 its reverse (42734212), we get a palindrome (63977936).

The spelling of 21243724 in words is "twenty-one million, two hundred forty-three thousand, seven hundred twenty-four".