21530500 has 72 divisors (see below), whose sum is σ = 50286600. Its totient is φ = 8051200.

The previous prime is 21530497. The next prime is 21530513. The reversal of 21530500 is 503512.

21530500 is nontrivially palindromic in base 13.

It can be written as a sum of positive squares in 12 ways, for example, as 13645636 + 7884864 = 3694^2 + 2808^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 144426 + ... + 144574.

It is an arithmetic number, because the mean of its divisors is an integer number (698425).

Almost surely, 2^21530500 is an apocalyptic number.

21530500 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 21530500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25143300).

21530500 is an abundant number, since it is smaller than the sum of its proper divisors (28756100).

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

21530500 is a wasteful number, since it uses less digits than its factorization.

21530500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 202 (or 173 counting only the distinct ones).

The product of its (nonzero) digits is 150, while the sum is 16.

The square root of 21530500 is about 4640.0969817451. The cubic root of 21530500 is about 278.1963142465.

The spelling of 21530500 in words is "twenty-one million, five hundred thirty thousand, five hundred".