21100123 has 4 divisors (see below), whose sum is σ = 23018328. Its totient is φ = 19181920.

The previous prime is 21100103. The next prime is 21100129. The reversal of 21100123 is 32100112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21100123 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21100129) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 959086 + ... + 959107.

It is an arithmetic number, because the mean of its divisors is an integer number (5754582).

Almost surely, 2^21100123 is an apocalyptic number.

21100123 is a deficient number, since it is larger than the sum of its proper divisors (1918205).

21100123 is a wasteful number, since it uses less digits than its factorization.

21100123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1918204.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21100123 is about 4593.4870196834. The cubic root of 21100123 is about 276.3301857683.

Adding to 21100123 its reverse (32100112), we get a palindrome (53200235).

The spelling of 21100123 in words is "twenty-one million, one hundred thousand, one hundred twenty-three".