221805 has 32 divisors (see below), whose sum is σ = 414720. Its totient is φ = 112320.

The previous prime is 221797. The next prime is 221807. The reversal of 221805 is 508122.

221805 = T₄ + T₅ + ... + T₁₀₉.

It is not a de Polignac number, because 221805 - 2³ = 221797 is a prime.

It is an Ulam number.

221805 is a lucky number.

It is a zygodrome in base 8.

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 221805.

It is not an unprimeable number, because it can be changed into a prime (221807) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4159 + ... + 4211.

It is an arithmetic number, because the mean of its divisors is an integer number (12960).

2²²¹⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

221805 is a deficient number, since it is larger than the sum of its proper divisors (192915).

221805 is a wasteful number, since it uses less digits than its factorization.

221805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 98 (or 92 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 18.

The square root of 221805 is about 470.9617818889. The cubic root of 221805 is about 60.5327555248.

Adding to 221805 its reverse (508122), we get a palindrome (729927).

The spelling of 221805 in words is "two hundred twenty-one thousand, eight hundred five".