21108720 has 80 divisors (see below), whose sum is σ = 65879712. Its totient is φ = 5591040.

The previous prime is 21108707. The next prime is 21108749. The reversal of 21108720 is 2780112.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 67284 + ... + 67596.

Almost surely, 2^21108720 is an apocalyptic number.

21108720 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 21108720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32939856).

21108720 is an abundant number, since it is smaller than the sum of its proper divisors (44770992).

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

21108720 is a wasteful number, since it uses less digits than its factorization.

21108720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 610 (or 604 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 21.

The square root of 21108720 is about 4594.4227058467. The cubic root of 21108720 is about 276.3677098472.

Adding to 21108720 its reverse (2780112), we get a palindrome (23888832).

The spelling of 21108720 in words is "twenty-one million, one hundred eight thousand, seven hundred twenty".