21125720 has 128 divisors (see below), whose sum is σ = 62553600. Its totient is φ = 6238080.

The previous prime is 21125711. The next prime is 21125723. The reversal of 21125720 is 2752112.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21125692 and 21125701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21125723) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1111871 + ... + 1111889.

It is an arithmetic number, because the mean of its divisors is an integer number (488700).

Almost surely, 2^21125720 is an apocalyptic number.

21125720 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 21125720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31276800).

21125720 is an abundant number, since it is smaller than the sum of its proper divisors (41427880).

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

21125720 is a wasteful number, since it uses less digits than its factorization.

21125720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86 (or 44 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21125720 is about 4596.2724027194. The cubic root of 21125720 is about 276.4418812541.

Adding to 21125720 its reverse (2752112), we get a palindrome (23877832).

It can be divided in two parts, 21125 and 720, that multiplied together give a square (15210000 = 3900²).

The spelling of 21125720 in words is "twenty-one million, one hundred twenty-five thousand, seven hundred twenty".