135981 has 12 divisors (see below), whose sum is σ = 203580. Its totient is φ = 87360.

The previous prime is 135979. The next prime is 136013. The reversal of 135981 is 189531.

135981 is a nontrivial binomial coefficient, being equal to C(522, 2).

It can be written as a sum of positive squares in 2 ways, for example, as 54756 + 81225 = 234^2 + 285^2 .

It is not a de Polignac number, because 135981 - 2¹ = 135979 is a prime.

It is a super-2 number, since 2×135981² = 36981664722, which contains 22 as substring.

It is an Ulam number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (135911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1 + ... + 521.

It is an arithmetic number, because the mean of its divisors is an integer number (16965).

2¹³⁵⁹⁸¹ is an apocalyptic number.

135981 is the 521-st triangular number and also the 261-st hexagonal number.

It is an amenable number.

135981 is a deficient number, since it is larger than the sum of its proper divisors (67599).

135981 is a wasteful number, since it uses less digits than its factorization.

135981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 556 (or 553 counting only the distinct ones).

The product of its digits is 1080, while the sum is 27.

The square root of 135981 is about 368.7560169001. The cubic root of 135981 is about 51.4232368805.

The spelling of 135981 in words is "one hundred thirty-five thousand, nine hundred eighty-one".