135981581 has 4 divisors (see below), whose sum is σ = 136187964. Its totient is φ = 135775200.

The previous prime is 135981557. The next prime is 135981583. The reversal of 135981581 is 185189531.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 185189531 = 2693 ⋅68767.

It can be written as a sum of positive squares in 2 ways, for example, as 103022500 + 32959081 = 10150^2 + 5741^2 .

It is a cyclic number.

It is not a de Polignac number, because 135981581 - 2²² = 131787277 is a prime.

It is a super-2 number, since 2×135981581² = 36981980742519122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (135981583) 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, 102200 + ... + 103521.

It is an arithmetic number, because the mean of its divisors is an integer number (34046991).

Almost surely, 2^135981581 is an apocalyptic number.

It is an amenable number.

135981581 is a deficient number, since it is larger than the sum of its proper divisors (206383).

135981581 is an equidigital number, since it uses as much as digits as its factorization.

135981581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 206382.

The product of its digits is 43200, while the sum is 41.

The square root of 135981581 is about 11661.1140548406. The cubic root of 135981581 is about 514.2331011837.

The spelling of 135981581 in words is "one hundred thirty-five million, nine hundred eighty-one thousand, five hundred eighty-one".