181721 has 2 divisors, whose sum is σ = 181722. Its totient is φ = 181720.

The previous prime is 181717. The next prime is 181729. The reversal of 181721 is 127181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 126025 + 55696 = 355^2 + 236^2 .

It is a cyclic number.

It is not a de Polignac number, because 181721 - 2² = 181717 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 181693 and 181702.

It is not a weakly prime, because it can be changed into another prime (181729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 90860 + 90861.

It is an arithmetic number, because the mean of its divisors is an integer number (90861).

2¹⁸¹⁷²¹ is an apocalyptic number.

It is an amenable number.

181721 is a deficient number, since it is larger than the sum of its proper divisors (1).

181721 is an equidigital number, since it uses as much as digits as its factorization.

181721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 112, while the sum is 20.

The square root of 181721 is about 426.2874616969. The cubic root of 181721 is about 56.6415382627.

The spelling of 181721 in words is "one hundred eighty-one thousand, seven hundred twenty-one".