199721 has 2 divisors, whose sum is σ = 199722. Its totient is φ = 199720.

The previous prime is 199697. The next prime is 199729. The reversal of 199721 is 127991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 151321 + 48400 = 389^2 + 220^2 .

It is a cyclic number.

It is not a de Polignac number, because 199721 - 2⁶ = 199657 is a prime.

It is not a weakly prime, because it can be changed into another prime (199729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99860 + 99861.

It is an arithmetic number, because the mean of its divisors is an integer number (99861).

2¹⁹⁹⁷²¹ is an apocalyptic number.

It is an amenable number.

199721 is a deficient number, since it is larger than the sum of its proper divisors (1).

199721 is an equidigital number, since it uses as much as digits as its factorization.

199721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1134, while the sum is 29.

The square root of 199721 is about 446.9015551550. The cubic root of 199721 is about 58.4531487446.

The spelling of 199721 in words is "one hundred ninety-nine thousand, seven hundred twenty-one".