20987813 has 24 divisors (see below), whose sum is σ = 26812800. Its totient is φ = 16077600.

The previous prime is 20987807. The next prime is 20987821. The reversal of 20987813 is 31878902.

It is not a de Polignac number, because 20987813 - 2⁴ = 20987797 is a prime.

It is a Curzon number.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20987873) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 59963 + ... + 60311.

It is an arithmetic number, because the mean of its divisors is an integer number (1117200).

Almost surely, 2^20987813 is an apocalyptic number.

It is an amenable number.

20987813 is a deficient number, since it is larger than the sum of its proper divisors (5824987).

20987813 is a wasteful number, since it uses less digits than its factorization.

20987813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 449 (or 438 counting only the distinct ones).

The product of its (nonzero) digits is 24192, while the sum is 38.

The square root of 20987813 is about 4581.2457912668. The cubic root of 20987813 is about 275.8390374552.

The spelling of 20987813 in words is "twenty million, nine hundred eighty-seven thousand, eight hundred thirteen".