21128704 has 40 divisors (see below), whose sum is σ = 43702560. Its totient is φ = 10192896.

The previous prime is 21128693. The next prime is 21128719. The reversal of 21128704 is 40782112.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14137 + ... + 15559.

It is an arithmetic number, because the mean of its divisors is an integer number (1092564).

Almost surely, 2^21128704 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21128704, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21851280).

21128704 is an abundant number, since it is smaller than the sum of its proper divisors (22573856).

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

21128704 is an equidigital number, since it uses as much as digits as its factorization.

21128704 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1470 (or 1454 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21128704 is about 4596.5970021310. The cubic root of 21128704 is about 276.4548964119.

It can be divided in two parts, 2112 and 8704, that added together give a square (10816 = 104²).

The spelling of 21128704 in words is "twenty-one million, one hundred twenty-eight thousand, seven hundred four".