20921999 has 8 divisors (see below), whose sum is σ = 23940000. Its totient is φ = 17911296.

The previous prime is 20921987. The next prime is 20922017. The reversal of 20921999 is 99912902.

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

It is a cyclic number.

It is not a de Polignac number, because 20921999 - 2²⁴ = 4144783 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921959) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7547 + ... + 9939.

It is an arithmetic number, because the mean of its divisors is an integer number (2992500).

Almost surely, 2^20921999 is an apocalyptic number.

20921999 is a deficient number, since it is larger than the sum of its proper divisors (3018001).

20921999 is a wasteful number, since it uses less digits than its factorization.

20921999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3649.

The product of its (nonzero) digits is 26244, while the sum is 41.

The square root of 20921999 is about 4574.0571706090. The cubic root of 20921999 is about 275.5504083747.

The spelling of 20921999 in words is "twenty million, nine hundred twenty-one thousand, nine hundred ninety-nine".