21000724 has 6 divisors (see below), whose sum is σ = 36751274. Its totient is φ = 10500360.

The previous prime is 21000709. The next prime is 21000731. The reversal of 21000724 is 42700012.

It can be written as a sum of positive squares in only one way, i.e., 16548624 + 4452100 = 4068^2 + 2110^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21000698 and 21000707.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2625087 + ... + 2625094.

Almost surely, 2^21000724 is an apocalyptic number.

It is an amenable number.

21000724 is a deficient number, since it is larger than the sum of its proper divisors (15750550).

21000724 is a wasteful number, since it uses less digits than its factorization.

21000724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5250185 (or 5250183 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 16.

The square root of 21000724 is about 4582.6546891513. The cubic root of 21000724 is about 275.8955881749.

Adding to 21000724 its reverse (42700012), we get a palindrome (63700736).

The spelling of 21000724 in words is "twenty-one million, seven hundred twenty-four", and thus it is an aban number.