21210890 has 16 divisors (see below), whose sum is σ = 39496680. Its totient is φ = 8191680.

The previous prime is 21210881. The next prime is 21210901. The reversal of 21210890 is 9801212.

It can be written as a sum of positive squares in 4 ways, for example, as 19811401 + 1399489 = 4451^2 + 1183^2 .

It is a Curzon number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 36281 + ... + 36860.

Almost surely, 2^21210890 is an apocalyptic number.

21210890 is a deficient number, since it is larger than the sum of its proper divisors (18285790).

21210890 is a wasteful number, since it uses less digits than its factorization.

21210890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73177.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 21210890 is about 4605.5281998920. The cubic root of 21210890 is about 276.8128821814.

The spelling of 21210890 in words is "twenty-one million, two hundred ten thousand, eight hundred ninety".