21456720 has 120 divisors (see below), whose sum is σ = 76341096. Its totient is φ = 5382144.

The previous prime is 21456713. The next prime is 21456727. The reversal of 21456720 is 2765412.

It is an interprime number because it is at equal distance from previous prime (21456713) and next prime (21456727).

It can be written as a sum of positive squares in 4 ways, for example, as 553536 + 20903184 = 744^2 + 4572^2 .

It is a tau number, because it is divible by the number of its divisors (120).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21456727) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 11364 + ... + 13116.

Almost surely, 2^21456720 is an apocalyptic number.

21456720 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 21456720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38170548).

21456720 is an abundant number, since it is smaller than the sum of its proper divisors (54884376).

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

21456720 is a wasteful number, since it uses less digits than its factorization.

21456720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1789 (or 1780 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 27.

The square root of 21456720 is about 4632.1398942605. The cubic root of 21456720 is about 277.8781792911.

The spelling of 21456720 in words is "twenty-one million, four hundred fifty-six thousand, seven hundred twenty".