221815 has 16 divisors (see below), whose sum is σ = 300960. Its totient is φ = 155520.

The previous prime is 221813. The next prime is 221827. The reversal of 221815 is 518122.

221815 = T₁ + T₂ + ... + T₁₀₉.

221815 is a nontrivial binomial coefficient, being equal to C(111, 3).

It is not a de Polignac number, because 221815 - 2¹ = 221813 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 221792 and 221801.

It is a congruent number.

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

It is the 109-th tetrahedral number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1981 + ... + 2089.

It is an arithmetic number, because the mean of its divisors is an integer number (18810).

2²²¹⁸¹⁵ is an apocalyptic number.

221815 is a deficient number, since it is larger than the sum of its proper divisors (79145).

221815 is a wasteful number, since it uses less digits than its factorization.

221815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162.

The product of its digits is 160, while the sum is 19.

The square root of 221815 is about 470.9723983420. The cubic root of 221815 is about 60.5336652104.

Adding to 221815 its reverse (518122), we get a palindrome (739937).

The spelling of 221815 in words is "two hundred twenty-one thousand, eight hundred fifteen".