21131880 has 128 divisors (see below), whose sum is σ = 79073280. Its totient is φ = 4389120.

The previous prime is 21131827. The next prime is 21131881. The reversal of 21131880 is 8813112.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21131880.

It is not an unprimeable number, because it can be changed into a prime (21131881) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 8097 + ... + 10383.

It is an arithmetic number, because the mean of its divisors is an integer number (617760).

Almost surely, 2^21131880 is an apocalyptic number.

21131880 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 21131880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39536640).

21131880 is an abundant number, since it is smaller than the sum of its proper divisors (57941400).

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

21131880 is a wasteful number, since it uses less digits than its factorization.

21131880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2319 (or 2315 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 24.

The square root of 21131880 is about 4596.9424621154. The cubic root of 21131880 is about 276.4687476599.

Adding to 21131880 its reverse (8813112), we get a palindrome (29944992).

It can be divided in two parts, 2113 and 1880, that added together give a palindrome (3993).

The spelling of 21131880 in words is "twenty-one million, one hundred thirty-one thousand, eight hundred eighty".