20991801 has 16 divisors (see below), whose sum is σ = 29583360. Its totient is φ = 13213200.

The previous prime is 20991799. The next prime is 20991809. The reversal of 20991801 is 10819902.

It is not a de Polignac number, because 20991801 - 2¹ = 20991799 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20991809) 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 15 ways as a sum of consecutive naturals, for example, 3526 + ... + 7376.

It is an arithmetic number, because the mean of its divisors is an integer number (1848960).

Almost surely, 2^20991801 is an apocalyptic number.

It is an amenable number.

20991801 is a deficient number, since it is larger than the sum of its proper divisors (8591559).

20991801 is a wasteful number, since it uses less digits than its factorization.

20991801 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3956.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 20991801 is about 4581.6810233800. The cubic root of 20991801 is about 275.8565075368.

The spelling of 20991801 in words is "twenty million, nine hundred ninety-one thousand, eight hundred one".