20999891 has 4 divisors (see below), whose sum is σ = 22908984. Its totient is φ = 19090800.

The previous prime is 20999887. The next prime is 20999893. The reversal of 20999891 is 19899902.

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 20999891 - 2² = 20999887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20999893) 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, 954530 + ... + 954551.

It is an arithmetic number, because the mean of its divisors is an integer number (5727246).

Almost surely, 2^20999891 is an apocalyptic number.

20999891 is a deficient number, since it is larger than the sum of its proper divisors (1909093).

20999891 is a wasteful number, since it uses less digits than its factorization.

20999891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1909092.

The product of its (nonzero) digits is 104976, while the sum is 47.

The square root of 20999891 is about 4582.5638020654. The cubic root of 20999891 is about 275.8919402996.

The spelling of 20999891 in words is "twenty million, nine hundred ninety-nine thousand, eight hundred ninety-one".