16381 has 2 divisors, whose sum is σ = 16382. Its totient is φ = 16380.

The previous prime is 16369. The next prime is 16411. The reversal of 16381 is 18361.

16381 = T₁₀₃ + T₁₀₄ + T₁₀₅.

16381 = 90² + 91².

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8281 + 8100 = 91^2 + 90^2 .

It is a cyclic number.

It is not a de Polignac number, because 16381 - 2⁵ = 16349 is a prime.

It is a super-2 number, since 2×16381² = 536674322, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

16381 is a lucky number.

It is a nialpdrome in base 4 and base 7.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8190 + 8191.

It is an arithmetic number, because the mean of its divisors is an integer number (8191).

16381 is a Friedman number, since it can be written as (1+1)^(8+6)-3, using all its digits and the basic arithmetic operations.

2¹⁶³⁸¹ is an apocalyptic number.

16381 is the 105-th centered triangular number and also the 91-st centered square number.

It is an amenable number.

16381 is a deficient number, since it is larger than the sum of its proper divisors (1).

16381 is an equidigital number, since it uses as much as digits as its factorization.

16381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 144, while the sum is 19.

The square root of 16381 is about 127.9882807135. The cubic root of 16381 is about 25.3968665405.

It can be divided in two parts, 163 and 81, that multiplied together give a triangular number (13203 = T₁₆₂).

The spelling of 16381 in words is "sixteen thousand, three hundred eighty-one".