221904 has 60 divisors (see below), whose sum is σ = 657696. Its totient is φ = 69696.

The previous prime is 221891. The next prime is 221909. The reversal of 221904 is 409122.

221904 = 87² + 88² + ... + 109².

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221909) by changing a digit.

221904 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3279 + ... + 3345.

2²²¹⁹⁰⁴ is an apocalyptic number.

221904 is a gapful number since it is divisible by the number (24) 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 221904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (328848).

221904 is an abundant number, since it is smaller than the sum of its proper divisors (435792).

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

221904 is a wasteful number, since it uses less digits than its factorization.

221904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104 (or 95 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 221904 is about 471.0668742334. The cubic root of 221904 is about 60.5417602082.

The spelling of 221904 in words is "two hundred twenty-one thousand, nine hundred four".