199681 has 4 divisors (see below), whose sum is σ = 200772. Its totient is φ = 198592.

The previous prime is 199679. The next prime is 199687. The reversal of 199681 is 186991.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 186991 = 7 ⋅26713.

It can be written as a sum of positive squares in 2 ways, for example, as 119025 + 80656 = 345^2 + 284^2 .

It is a cyclic number.

It is not a de Polignac number, because 199681 - 2¹ = 199679 is a prime.

It is a super-2 number, since 2×199681² = 79745003522, which contains 22 as substring.

It is a Duffinian number.

199681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (199687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 196 + ... + 661.

It is an arithmetic number, because the mean of its divisors is an integer number (50193).

It is a Proth number, since it is equal to 195 ⋅ 2¹⁰ + 1 and 195 < 2¹⁰.

2¹⁹⁹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

199681 is a deficient number, since it is larger than the sum of its proper divisors (1091).

199681 is an equidigital number, since it uses as much as digits as its factorization.

199681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1090.

The product of its digits is 3888, while the sum is 34.

The square root of 199681 is about 446.8568003287. The cubic root of 199681 is about 58.4492461637.

The spelling of 199681 in words is "one hundred ninety-nine thousand, six hundred eighty-one".