129 (one hundred [and] twenty-nine) is the natural number following 128 and preceding 130.
129 is the sum of the first ten prime numbers. It is the smallest number that can be expressed as a sum of three squares in four different ways: , , , and .
129 is the product of only two primes, 3 and 43, making 129 a semiprime. Since 3 and 43 are both Gaussian primes, this means that 129 is a Blum integer.
129 is a repdigit in base 6 (333).
129 is a happy number.
129 is a centered octahedral number.