221728 has 36 divisors (see below), whose sum is σ = 484218. Its totient is φ = 99840.

The previous prime is 221723. The next prime is 221729. The reversal of 221728 is 827122.

It can be written as a sum of positive squares in 3 ways, for example, as 51984 + 169744 = 228^2 + 412^2 .

Its product of digits (448) is a multiple of the sum of its prime divisors (56).

It is a junction number, because it is equal to n+sod(n) for n = 221699 and 221708.

It is not an unprimeable number, because it can be changed into a prime (221723) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 5388 + ... + 5428.

2²²¹⁷²⁸ 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 221728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (242109).

221728 is an abundant number, since it is smaller than the sum of its proper divisors (262490).

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

221728 is a wasteful number, since it uses less digits than its factorization.

221728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77 (or 56 counting only the distinct ones).

The product of its digits is 448, while the sum is 22.

The square root of 221728 is about 470.8800271831. The cubic root of 221728 is about 60.5257500295.

It can be divided in two parts, 221 and 728, that added together give a palindrome (949).

The spelling of 221728 in words is "two hundred twenty-one thousand, seven hundred twenty-eight".