21235720 has 96 divisors (see below), whose sum is σ = 55702080. Its totient is φ = 7224320.

The previous prime is 21235657. The next prime is 21235723. The reversal of 21235720 is 2753212.

21235720 is nontrivially palindromic in base 9.

It is a Harshad number since it is a multiple of its sum of digits (22).

It is a junction number, because it is equal to n+sod(n) for n = 21235691 and 21235700.

It is not an unprimeable number, because it can be changed into a prime (21235723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 127077 + ... + 127243.

It is an arithmetic number, because the mean of its divisors is an integer number (580230).

Almost surely, 2^21235720 is an apocalyptic number.

21235720 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 21235720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27851040).

21235720 is an abundant number, since it is smaller than the sum of its proper divisors (34466360).

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

21235720 is a wasteful number, since it uses less digits than its factorization.

21235720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 223 (or 202 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 22.

The square root of 21235720 is about 4608.2230848777. The cubic root of 21235720 is about 276.9208547622.

Adding to 21235720 its reverse (2753212), we get a palindrome (23988932).

The spelling of 21235720 in words is "twenty-one million, two hundred thirty-five thousand, seven hundred twenty".