21005500 has 48 divisors (see below), whose sum is σ = 46990944. Its totient is φ = 8198400.

The previous prime is 21005477. The next prime is 21005503. The reversal of 21005500 is 550012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005503) 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, 21012 + ... + 21988.

It is an arithmetic number, because the mean of its divisors is an integer number (978978).

Almost surely, 2^21005500 is an apocalyptic number.

21005500 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 21005500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23495472).

21005500 is an abundant number, since it is smaller than the sum of its proper divisors (25985444).

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

21005500 is a wasteful number, since it uses less digits than its factorization.

21005500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1039 (or 1027 counting only the distinct ones).

The product of its (nonzero) digits is 50, while the sum is 13.

The square root of 21005500 is about 4583.1757548669. The cubic root of 21005500 is about 275.9165013817.

Adding to 21005500 its reverse (550012), we get a palindrome (21555512).

The spelling of 21005500 in words is "twenty-one million, five thousand, five hundred".