221816 has 32 divisors (see below), whose sum is σ = 505440. Its totient is φ = 89088.

The previous prime is 221813. The next prime is 221827. The reversal of 221816 is 618122.

221816 = 175² + 176² + ... + 181².

221816 is digitally balanced in base 2 and base 3, because in such bases it contains all the possibile digits an equal number of times.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 221816.

It is not an unprimeable number, because it can be changed into a prime (221813) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 836 + ... + 1068.

It is an arithmetic number, because the mean of its divisors is an integer number (15795).

2²²¹⁸¹⁶ 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 221816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (252720).

221816 is an abundant number, since it is smaller than the sum of its proper divisors (283624).

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

221816 is a wasteful number, since it uses less digits than its factorization.

221816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 263 (or 259 counting only the distinct ones).

The product of its digits is 192, while the sum is 20.

The square root of 221816 is about 470.9734599741. The cubic root of 221816 is about 60.5337561775.

Adding to 221816 its reverse (618122), we get a palindrome (839938).

The spelling of 221816 in words is "two hundred twenty-one thousand, eight hundred sixteen".