21205500 has 96 divisors (see below), whose sum is σ = 62969088. Its totient is φ = 5544000.

The previous prime is 21205453. The next prime is 21205523. The reversal of 21205500 is 550212.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21205500.

It is a congruent number.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 100395 + ... + 100605.

It is an arithmetic number, because the mean of its divisors is an integer number (655928).

Almost surely, 2^21205500 is an apocalyptic number.

21205500 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 21205500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31484544).

21205500 is an abundant number, since it is smaller than the sum of its proper divisors (41763588).

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

21205500 is a wasteful number, since it uses less digits than its factorization.

21205500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 300 (or 288 counting only the distinct ones).

The product of its (nonzero) digits is 100, while the sum is 15.

The square root of 21205500 is about 4604.9429963899. The cubic root of 21205500 is about 276.7894327829.

Adding to 21205500 its reverse (550212), we get a palindrome (21755712).

The spelling of 21205500 in words is "twenty-one million, two hundred five thousand, five hundred".