21316720 has 80 divisors (see below), whose sum is σ = 52059168. Its totient is φ = 8110080.

The previous prime is 21316693. The next prime is 21316721. The reversal of 21316720 is 2761312.

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

It is a junction number, because it is equal to n+sod(n) for n = 21316691 and 21316700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21316721) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 219712 + ... + 219808.

Almost surely, 2^21316720 is an apocalyptic number.

21316720 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 21316720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26029584).

21316720 is an abundant number, since it is smaller than the sum of its proper divisors (30742448).

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

21316720 is a wasteful number, since it uses less digits than its factorization.

21316720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 218 (or 212 counting only the distinct ones).

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 21316720 is about 4617.0033571571. The cubic root of 21316720 is about 277.2724970314.

The spelling of 21316720 in words is "twenty-one million, three hundred sixteen thousand, seven hundred twenty".