123 has 4 divisors (see below), whose sum is σ = 168. Its totient is φ = 80.

The previous prime is 113. The next prime is 127. The reversal of 123 is 321.

Adding to 123 its reverse (321), we get a palindrome (444).

It can be divided in two parts, 12 and 3, that multiplied together give a triangular number (36 = T_{8}).

123 is nontrivially palindromic in base 6.

123 is an esthetic number in base 6, base 7 and base 10, because in such bases its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 321 = 3 ⋅107.

It is a cyclic number.

It is not a de Polignac number, because 123 - 2^{4} = 107 is a prime.

It is a Lucas number.

It is a D-number.

It is an alternating number because its digits alternate between odd and even.

123 is an undulating number in base 6.

It is a straight-line number, since its digits are in arithmetic progression.

It is a plaindrome in base 7, base 9, base 10, base 14 and base 16.

It is a nialpdrome in base 5, base 12, base 13 and base 15.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18 + ... + 23.

It is an arithmetic number, because the mean of its divisors is an integer number (42).

123 is a deficient number, since it is larger than the sum of its proper divisors (45).

123 is an equidigital number, since it uses as much as digits as its factorization.

123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 44.

The product of its digits is 6, while the sum is 6.

The square root of 123 is about 11.0905365064. The cubic root of 123 is about 4.9731898333.

The spelling of 123 in words is "one hundred twenty-three", and thus it is an aban number and an iban number.

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