221681 has 4 divisors (see below), whose sum is σ = 228864. Its totient is φ = 214500.

The previous prime is 221677. The next prime is 221707. The reversal of 221681 is 186122.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 221681 - 2² = 221677 is a prime.

It is a super-2 number, since 2×221681² = 98284931522, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon 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, 3545 + ... + 3606.

It is an arithmetic number, because the mean of its divisors is an integer number (57216).

2²²¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

221681 is a deficient number, since it is larger than the sum of its proper divisors (7183).

221681 is an equidigital number, since it uses as much as digits as its factorization.

221681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7182.

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

The square root of 221681 is about 470.8301179831. The cubic root of 221681 is about 60.5214731508.

The spelling of 221681 in words is "two hundred twenty-one thousand, six hundred eighty-one".