21809100 has 72 divisors (see below), whose sum is σ = 63676480. Its totient is φ = 5762880.

The previous prime is 21809087. The next prime is 21809101. The reversal of 21809100 is 190812.

It is not an unprimeable number, because it can be changed into a prime (21809101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 41439 + ... + 41961.

Almost surely, 2^21809100 is an apocalyptic number.

21809100 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 21809100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31838240).

21809100 is an abundant number, since it is smaller than the sum of its proper divisors (41867380).

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

21809100 is a wasteful number, since it uses less digits than its factorization.

21809100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 679 (or 672 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 21.

The square root of 21809100 is about 4670.0214132271. The cubic root of 21809100 is about 279.3911088310.

Adding to 21809100 its reverse (190812), we get a palindrome (21999912).

The spelling of 21809100 in words is "twenty-one million, eight hundred nine thousand, one hundred".