20991880 has 128 divisors (see below), whose sum is σ = 59673600. Its totient is φ = 6469632.

The previous prime is 20991863. The next prime is 20991899. The reversal of 20991880 is 8819902.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 265681 + ... + 265759.

It is an arithmetic number, because the mean of its divisors is an integer number (466200).

Almost surely, 2^20991880 is an apocalyptic number.

20991880 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20991880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29836800).

20991880 is an abundant number, since it is smaller than the sum of its proper divisors (38681720).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20991880 is a wasteful number, since it uses less digits than its factorization.

20991880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 183 (or 179 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 37.

The square root of 20991880 is about 4581.6896446617. The cubic root of 20991880 is about 275.8568535867.

The spelling of 20991880 in words is "twenty million, nine hundred ninety-one thousand, eight hundred eighty".