21601728 has 98 divisors (see below), whose sum is σ = 64408304. Its totient is φ = 7185024.

The previous prime is 21601721. The next prime is 21601757. The reversal of 21601728 is 82710612.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21601721) by changing a digit.

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 13 ways as a sum of consecutive naturals, for example, 46425 + ... + 46887.

Almost surely, 2^21601728 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21601728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32204152).

21601728 is an abundant number, since it is smaller than the sum of its proper divisors (42806576).

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

21601728 is an frugal number, since it uses more digits than its factorization.

21601728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 493 (or 468 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21601728 is about 4647.7659149316. The cubic root of 21601728 is about 278.5027563609.

The spelling of 21601728 in words is "twenty-one million, six hundred one thousand, seven hundred twenty-eight".