21058921 has 9 divisors (see below), whose sum is σ = 22868229. Its totient is φ = 19383936.

The previous prime is 21058907. The next prime is 21058931. The reversal of 21058921 is 12985012.

The square root of 21058921 is 4589.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 4575321 + 16483600 = 2139^2 + 4060^2 .

It is not a de Polignac number, because 21058921 - 2¹¹ = 21056873 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21058921.

It is not an unprimeable number, because it can be changed into a prime (21058931) 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 8 ways as a sum of consecutive naturals, for example, 59481 + ... + 59833.

Almost surely, 2^21058921 is an apocalyptic number.

21058921 is the 4589-th square number.

21058921 is the 2295-th centered octagonal number.

It is an amenable number.

21058921 is a deficient number, since it is larger than the sum of its proper divisors (1809308).

21058921 is an frugal number, since it uses more digits than its factorization.

21058921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 732 (or 366 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 28.

The cubic root of 21058921 is about 276.1502061689.

It can be divided in two parts, 2105 and 8921, that added together give a triangular number (11026 = T₁₄₈).

The spelling of 21058921 in words is "twenty-one million, fifty-eight thousand, nine hundred twenty-one".