21125220 has 96 divisors (see below), whose sum is σ = 63504000. Its totient is φ = 5228544.

The previous prime is 21125219. The next prime is 21125227. The reversal of 21125220 is 2252112.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21125220.

It is not an unprimeable number, because it can be changed into a prime (21125227) 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, 141706 + ... + 141854.

It is an arithmetic number, because the mean of its divisors is an integer number (661500).

Almost surely, 2^21125220 is an apocalyptic number.

21125220 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 21125220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31752000).

21125220 is an abundant number, since it is smaller than the sum of its proper divisors (42378780).

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

21125220 is a wasteful number, since it uses less digits than its factorization.

21125220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 317 (or 315 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21125220 is about 4596.2180104952. The cubic root of 21125220 is about 276.4397003102.

Adding to 21125220 its reverse (2252112), we get a palindrome (23377332).

The spelling of 21125220 in words is "twenty-one million, one hundred twenty-five thousand, two hundred twenty".