20931999 has 16 divisors (see below), whose sum is σ = 30792960. Its totient is φ = 12541760.

The previous prime is 20931949. The next prime is 20932003. The reversal of 20931999 is 99913902.

It is a happy number.

It is not a de Polignac number, because 20931999 - 2⁹ = 20931487 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20931999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20931949) 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 15 ways as a sum of consecutive naturals, for example, 627 + ... + 6500.

It is an arithmetic number, because the mean of its divisors is an integer number (1924560).

Almost surely, 2^20931999 is an apocalyptic number.

20931999 is a deficient number, since it is larger than the sum of its proper divisors (9860961).

20931999 is a wasteful number, since it uses less digits than its factorization.

20931999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7230.

The product of its (nonzero) digits is 39366, while the sum is 42.

The square root of 20931999 is about 4575.1501614701. The cubic root of 20931999 is about 275.5943026060.

The spelling of 20931999 in words is "twenty million, nine hundred thirty-one thousand, nine hundred ninety-nine".