21004253 has 16 divisors (see below), whose sum is σ = 23147520. Its totient is φ = 18987696.

The previous prime is 21004241. The next prime is 21004261. The reversal of 21004253 is 35240012.

It is a cyclic number.

It is not a de Polignac number, because 21004253 - 2⁴ = 21004237 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21004273) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38126 + ... + 38672.

It is an arithmetic number, because the mean of its divisors is an integer number (1446720).

Almost surely, 2^21004253 is an apocalyptic number.

It is an amenable number.

21004253 is a deficient number, since it is larger than the sum of its proper divisors (2143267).

21004253 is a wasteful number, since it uses less digits than its factorization.

21004253 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 656.

The product of its (nonzero) digits is 240, while the sum is 17.

The square root of 21004253 is about 4583.0397118070. The cubic root of 21004253 is about 275.9110413087.

Adding to 21004253 its reverse (35240012), we get a palindrome (56244265).

The spelling of 21004253 in words is "twenty-one million, four thousand, two hundred fifty-three".