21003657 has 16 divisors (see below), whose sum is σ = 28599168. Its totient is φ = 13708800.

The previous prime is 21003637. The next prime is 21003659. The reversal of 21003657 is 75630012.

It is not a de Polignac number, because 21003657 - 2¹⁹ = 20479369 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21003659) 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 15 ways as a sum of consecutive naturals, for example, 30873 + ... + 31545.

It is an arithmetic number, because the mean of its divisors is an integer number (1787448).

Almost surely, 2^21003657 is an apocalyptic number.

It is an amenable number.

21003657 is a deficient number, since it is larger than the sum of its proper divisors (7595511).

21003657 is a wasteful number, since it uses less digits than its factorization.

21003657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 880.

The product of its (nonzero) digits is 1260, while the sum is 24.

The square root of 21003657 is about 4582.9746889984. The cubic root of 21003657 is about 275.9084316065.

Adding to 21003657 its reverse (75630012), we get a palindrome (96633669).

The spelling of 21003657 in words is "twenty-one million, three thousand, six hundred fifty-seven".