21128500 has 24 divisors (see below), whose sum is σ = 46145736. Its totient is φ = 8451200.

The previous prime is 21128477. The next prime is 21128507. The reversal of 21128500 is 582112.

It can be written as a sum of positive squares in 4 ways, for example, as 824464 + 20304036 = 908^2 + 4506^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128507) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 20629 + ... + 21628.

It is an arithmetic number, because the mean of its divisors is an integer number (1922739).

Almost surely, 2^21128500 is an apocalyptic number.

21128500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21128500 is an abundant number, since it is smaller than the sum of its proper divisors (25017236).

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

21128500 is a wasteful number, since it uses less digits than its factorization.

21128500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42276 (or 42264 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 19.

The square root of 21128500 is about 4596.5748117484. The cubic root of 21128500 is about 276.4540066747.

The spelling of 21128500 in words is "twenty-one million, one hundred twenty-eight thousand, five hundred".