221691 has 4 divisors (see below), whose sum is σ = 295592. Its totient is φ = 147792.

The previous prime is 221677. The next prime is 221707. The reversal of 221691 is 196122.

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

It is not a de Polignac number, because 221691 - 2⁵ = 221659 is a prime.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221621) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36946 + ... + 36951.

It is an arithmetic number, because the mean of its divisors is an integer number (73898).

2²²¹⁶⁹¹ is an apocalyptic number.

221691 is a deficient number, since it is larger than the sum of its proper divisors (73901).

221691 is an equidigital number, since it uses as much as digits as its factorization.

221691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73900.

The product of its digits is 216, while the sum is 21.

The square root of 221691 is about 470.8407374049. The cubic root of 221691 is about 60.5223831757.

The spelling of 221691 in words is "two hundred twenty-one thousand, six hundred ninety-one".