221818 has 4 divisors (see below), whose sum is σ = 332730. Its totient is φ = 110908.

The previous prime is 221813. The next prime is 221827. The reversal of 221818 is 818122.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 165649 + 56169 = 407^2 + 237^2 .

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

221818 is a modest number, since divided by 1818 gives 22 as remainder.

It is a plaindrome in base 15.

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 as a sum of consecutive naturals, namely, 55453 + ... + 55456.

2²²¹⁸¹⁸ is an apocalyptic number.

221818 is a deficient number, since it is larger than the sum of its proper divisors (110912).

221818 is a wasteful number, since it uses less digits than its factorization.

221818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110911.

The product of its digits is 256, while the sum is 22.

The square root of 221818 is about 470.9755832312. The cubic root of 221818 is about 60.5339381108.

The spelling of 221818 in words is "two hundred twenty-one thousand, eight hundred eighteen".