133681 has 4 divisors (see below), whose sum is σ = 137332. Its totient is φ = 130032.

The previous prime is 133673. The next prime is 133691. The reversal of 133681 is 186331.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 186331 = 389 ⋅479.

It can be written as a sum of positive squares in 2 ways, for example, as 46656 + 87025 = 216^2 + 295^2 .

It is a cyclic number.

It is not a de Polignac number, because 133681 - 2³ = 133673 is a prime.

It is a super-2 number, since 2×133681² = 35741219522, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 9.

It is a nialpdrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (133631) 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, 1770 + ... + 1843.

It is an arithmetic number, because the mean of its divisors is an integer number (34333).

2¹³³⁶⁸¹ is an apocalyptic number.

It is an amenable number.

133681 is a deficient number, since it is larger than the sum of its proper divisors (3651).

133681 is an equidigital number, since it uses as much as digits as its factorization.

133681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3650.

The product of its digits is 432, while the sum is 22.

The square root of 133681 is about 365.6241239306. The cubic root of 133681 is about 51.1316603291.

Subtracting 133681 from its reverse (186331), we obtain a triangular number (52650 = T₃₂₄).

The spelling of 133681 in words is "one hundred thirty-three thousand, six hundred eighty-one".