21040123 has 4 divisors (see below), whose sum is σ = 22658608. Its totient is φ = 19421640.

The previous prime is 21040121. The next prime is 21040139. The reversal of 21040123 is 32104012.

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

It is a cyclic number.

It is not a de Polignac number, because 21040123 - 2¹ = 21040121 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13), and also a Moran number because the ratio is a prime number: 1618471 = 21040123 / (2 + 1 + 0 + 4 + 0 + 1 + 2 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21040121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 809223 + ... + 809248.

It is an arithmetic number, because the mean of its divisors is an integer number (5664652).

Almost surely, 2^21040123 is an apocalyptic number.

21040123 is a deficient number, since it is larger than the sum of its proper divisors (1618485).

21040123 is a wasteful number, since it uses less digits than its factorization.

21040123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1618484.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21040123 is about 4586.9513840894. The cubic root of 21040123 is about 276.0680142889.

Adding to 21040123 its reverse (32104012), we get a palindrome (53144135).

The spelling of 21040123 in words is "twenty-one million, forty thousand, one hundred twenty-three".