21606720 has 112 divisors (see below), whose sum is σ = 69787008. Its totient is φ = 5662720.

The previous prime is 21606719. The next prime is 21606727. The reversal of 21606720 is 2760612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21606727) 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, 68002 + ... + 68318.

Almost surely, 2^21606720 is an apocalyptic number.

21606720 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 21606720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34893504).

21606720 is an abundant number, since it is smaller than the sum of its proper divisors (48180288).

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

21606720 is a wasteful number, since it uses less digits than its factorization.

21606720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 408 (or 398 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 24.

The square root of 21606720 is about 4648.3029161190. The cubic root of 21606720 is about 278.5242080194.

The spelling of 21606720 in words is "twenty-one million, six hundred six thousand, seven hundred twenty".