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: 112 + 22 + 22 and 102 + 52 + 22 and 82 + 72 + 42.
However, it 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.