• 129 can be written using four 4's:
It is a happy number.
129 is nontrivially palindromic in base 2 and base 6.
129 is an esthetic number in base 12 and base 15, because in such bases its adjacent digits differ by 1.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 921 = 3 ⋅307.
It is a D-number.
It is an alternating number because its digits alternate between odd and even.
It is a Duffinian number.
129 is a lucky number.
129 is a nontrivial repdigit in base 6.
It is a plaindrome in base 6, base 10, base 13 and base 15.
It is a nialpdrome in base 6, base 12, base 14 and base 16.
It is a zygodrome in base 6.
It is an amenable number.
129 is an equidigital number, since it uses as much as digits as its factorization.
129 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 46.
The square root of 129 is about 11.3578166916. The cubic root of 129 is about 5.0527743472.
Adding to 129 its sum of digits (12), we get a palindrome (141).
Subtracting from 129 its product of digits (18), we obtain a palindrome (111).
The spelling of 129 in words is "one hundred twenty-nine", and thus it is an aban number.