129721 has 4 divisors (see below), whose sum is σ = 131572. Its totient is φ = 127872.

The previous prime is 129719. The next prime is 129733. The reversal of 129721 is 127921.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 69696 + 60025 = 264^2 + 245^2 .

It is a cyclic number.

It is not a de Polignac number, because 129721 - 2¹ = 129719 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 129692 and 129701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (129121) 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, 816 + ... + 961.

It is an arithmetic number, because the mean of its divisors is an integer number (32893).

2¹²⁹⁷²¹ is an apocalyptic number.

It is an amenable number.

129721 is a deficient number, since it is larger than the sum of its proper divisors (1851).

129721 is an equidigital number, since it uses as much as digits as its factorization.

129721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1850.

The product of its digits is 252, while the sum is 22.

The square root of 129721 is about 360.1680163479. The cubic root of 129721 is about 50.6217043020.

The spelling of 129721 in words is "one hundred twenty-nine thousand, seven hundred twenty-one".