21112720 has 20 divisors (see below), whose sum is σ = 49087260. Its totient is φ = 8445056.

The previous prime is 21112717. The next prime is 21112723. The reversal of 21112720 is 2721112.

It is an interprime number because it is at equal distance from previous prime (21112717) and next prime (21112723).

It can be written as a sum of positive squares in 2 ways, for example, as 11943936 + 9168784 = 3456^2 + 3028^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a junction number, because it is equal to n+sod(n) for n = 21112694 and 21112703.

It is not an unprimeable number, because it can be changed into a prime (21112723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131875 + ... + 132034.

It is an arithmetic number, because the mean of its divisors is an integer number (2454363).

Almost surely, 2^21112720 is an apocalyptic number.

21112720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21112720 is an abundant number, since it is smaller than the sum of its proper divisors (27974540).

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

21112720 is a wasteful number, since it uses less digits than its factorization.

21112720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 263922 (or 263916 counting only the distinct ones).

The product of its (nonzero) digits is 56, while the sum is 16.

The square root of 21112720 is about 4594.8579956295. The cubic root of 21112720 is about 276.3851655246.

Adding to 21112720 its reverse (2721112), we get a palindrome (23833832).

The spelling of 21112720 in words is "twenty-one million, one hundred twelve thousand, seven hundred twenty".