135781 has 2 divisors, whose sum is σ = 135782. Its totient is φ = 135780.

The previous prime is 135757. The next prime is 135787. The reversal of 135781 is 187531.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 70756 + 65025 = 266^2 + 255^2 .

It is an emirp because it is prime and its reverse (187531) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 135781 - 2¹¹ = 133733 is a prime.

It is a super-2 number, since 2×135781² = 36872959922, which contains 22 as substring.

135781 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (135787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 67890 + 67891.

It is an arithmetic number, because the mean of its divisors is an integer number (67891).

2¹³⁵⁷⁸¹ is an apocalyptic number.

It is an amenable number.

135781 is a deficient number, since it is larger than the sum of its proper divisors (1).

135781 is an equidigital number, since it uses as much as digits as its factorization.

135781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 840, while the sum is 25.

The square root of 135781 is about 368.4847350977. The cubic root of 135781 is about 51.3980135192.

The spelling of 135781 in words is "one hundred thirty-five thousand, seven hundred eighty-one".