221664 has 24 divisors (see below), whose sum is σ = 582120. Its totient is φ = 73856.

The previous prime is 221659. The next prime is 221671. The reversal of 221664 is 466122.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (24).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 221664.

It is a congruent number.

It is an unprimeable number.

221664 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 3 ways as a sum of consecutive naturals, for example, 1059 + ... + 1250.

It is an arithmetic number, because the mean of its divisors is an integer number (24255).

2²²¹⁶⁶⁴ is an apocalyptic number.

221664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

221664 is an abundant number, since it is smaller than the sum of its proper divisors (360456).

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

221664 is a wasteful number, since it uses less digits than its factorization.

221664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2322 (or 2314 counting only the distinct ones).

The product of its digits is 576, while the sum is 21.

The square root of 221664 is about 470.8120644164. The cubic root of 221664 is about 60.5199260459.

Adding to 221664 its reverse (466122), we get a palindrome (687786).

The spelling of 221664 in words is "two hundred twenty-one thousand, six hundred sixty-four".