21210387 has 8 divisors (see below), whose sum is σ = 30851520. Its totient is φ = 12854760.

The previous prime is 21210379. The next prime is 21210389. The reversal of 21210387 is 78301212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21210387 - 2³ = 21210379 is a prime.

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

It is not an unprimeable number, because it can be changed into a prime (21210389) 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 7 ways as a sum of consecutive naturals, for example, 321337 + ... + 321402.

It is an arithmetic number, because the mean of its divisors is an integer number (3856440).

Almost surely, 2^21210387 is an apocalyptic number.

21210387 is a deficient number, since it is larger than the sum of its proper divisors (9641133).

21210387 is a wasteful number, since it uses less digits than its factorization.

21210387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 642753.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21210387 is about 4605.4735912824. The cubic root of 21210387 is about 276.8106940290.

Adding to 21210387 its reverse (78301212), we get a palindrome (99511599).

The spelling of 21210387 in words is "twenty-one million, two hundred ten thousand, three hundred eighty-seven".