21809500 has 48 divisors (see below), whose sum is σ = 48589632. Its totient is φ = 8548800.

The previous prime is 21809477. The next prime is 21809503. The reversal of 21809500 is 590812.

It is a Harshad number since it is a multiple of its sum of digits (25).

It is a plaindrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21809503) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 26089 + ... + 26911.

It is an arithmetic number, because the mean of its divisors is an integer number (1012284).

Almost surely, 2^21809500 is an apocalyptic number.

21809500 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 21809500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24294816).

21809500 is an abundant number, since it is smaller than the sum of its proper divisors (26780132).

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

21809500 is a wasteful number, since it uses less digits than its factorization.

21809500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 895 (or 883 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 25.

The square root of 21809500 is about 4670.0642393869. The cubic root of 21809500 is about 279.3928169216.

The spelling of 21809500 in words is "twenty-one million, eight hundred nine thousand, five hundred".