20990987 has 4 divisors (see below), whose sum is σ = 21010200. Its totient is φ = 20971776.

The previous prime is 20990969. The next prime is 20991001. The reversal of 20990987 is 78909902.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20990987 - 2²⁴ = 4213771 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20990947) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7862 + ... + 10187.

It is an arithmetic number, because the mean of its divisors is an integer number (5252550).

Almost surely, 2^20990987 is an apocalyptic number.

20990987 is a deficient number, since it is larger than the sum of its proper divisors (19213).

20990987 is a wasteful number, since it uses less digits than its factorization.

20990987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19212.

The product of its (nonzero) digits is 81648, while the sum is 44.

The square root of 20990987 is about 4581.5921904945. The cubic root of 20990987 is about 275.8529418573.

The spelling of 20990987 in words is "twenty million, nine hundred ninety thousand, nine hundred eighty-seven".