• 129 can be written using four 4's:

129 has 4 divisors (see below), whose sum is σ = 176. Its totient is φ = 84.

The previous prime is 127. The next prime is 131. The reversal of 129 is 921.

It is a happy number.

129 is nontrivially palindromic in base 2 and base 6.

It is a Cunningham number, because it is equal to 2^{7}+1.

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 an interprime number because it is at equal distance from previous prime (127) and next prime (131).

It is not a de Polignac number, because 129 - 2^{1} = 127 is a prime.

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 a pernicious number, because its binary representation contains a prime number (2) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19 + ... + 24.

It is an arithmetic number, because the mean of its divisors is an integer number (44).

It is a Proth number, since it is equal to 1 ⋅ 2^{7} + 1 and 1 < 2^{7}.

It is an amenable number.

129 is a deficient number, since it is larger than the sum of its proper divisors (47).

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 product of its digits is 18, while the sum is 12.

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).

It can be divided in two parts, 12 and 9, that added together give a triangular number (21 = T_{6}).

The spelling of 129 in words is "one hundred twenty-nine", and thus it is an aban number.

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