129 (number)

129 (one hundred [and] twenty-nine) is the natural number following 128 and preceding 130.

← 128 129 130 →
← 120 121 122 123 124 125 126 127 128 129 → List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	one hundred twenty-nine
Ordinal	129th (one hundred twenty-ninth)
Factorization	3 × 43
Divisors	1, 3, 43, 129
Greek numeral	ΡΚΘ´
Roman numeral	CXXIX, cxxix
Binary	100000012
Ternary	112103
Senary	3336
Octal	2018
Duodecimal	A912
Hexadecimal	8116

In mathematics

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: ${\displaystyle 11^{2}+2^{2}+2^{2}}$, ${\displaystyle 10^{2}+5^{2}+2^{2}}$, ${\displaystyle 8^{2}+8^{2}+1^{2}}$, and ${\displaystyle 8^{2}+7^{2}+4^{2}}$.

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.^[1]

129 is a repdigit in base 6 (333).

129 is a happy number.^[2]

129 is a centered octahedral number.^[3]