129781 has 4 divisors (see below), whose sum is σ = 130572. Its totient is φ = 128992.

The previous prime is 129769. The next prime is 129793. The reversal of 129781 is 187921.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (129769) and next prime (129793).

It can be written as a sum of positive squares in 2 ways, for example, as 18225 + 111556 = 135^2 + 334^2 .

It is a cyclic number.

It is not a de Polignac number, because 129781 - 2⁵ = 129749 is a prime.

It is a super-2 number, since 2×129781² = 33686215922, which contains 22 as substring.

It is a Duffinian number.

129781 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (129281) 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 in 3 ways as a sum of consecutive naturals, for example, 46 + ... + 511.

It is an arithmetic number, because the mean of its divisors is an integer number (32643).

2¹²⁹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

129781 is a deficient number, since it is larger than the sum of its proper divisors (791).

129781 is an equidigital number, since it uses as much as digits as its factorization.

129781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 790.

The product of its digits is 1008, while the sum is 28.

The square root of 129781 is about 360.2513011774. The cubic root of 129781 is about 50.6295078036.

It can be divided in two parts, 1297 and 81, that added together give a triangular number (1378 = T₅₂).

The spelling of 129781 in words is "one hundred twenty-nine thousand, seven hundred eighty-one".