20021987 has 4 divisors (see below), whose sum is σ = 20122800. Its totient is φ = 19921176.

The previous prime is 20021951. The next prime is 20021999. The reversal of 20021987 is 78912002.

It is a happy number.

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 20021987 - 2⁸ = 20021731 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20021917) 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 3 ways as a sum of consecutive naturals, for example, 50108 + ... + 50505.

It is an arithmetic number, because the mean of its divisors is an integer number (5030700).

Almost surely, 2^20021987 is an apocalyptic number.

20021987 is a deficient number, since it is larger than the sum of its proper divisors (100813).

20021987 is a wasteful number, since it uses less digits than its factorization.

20021987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 100812.

The product of its (nonzero) digits is 2016, while the sum is 29.

The square root of 20021987 is about 4474.5935010904. The cubic root of 20021987 is about 271.5411950646.

Adding to 20021987 its reverse (78912002), we get a palindrome (98933989).

The spelling of 20021987 in words is "twenty million, twenty-one thousand, nine hundred eighty-seven".