21000123 has 6 divisors (see below), whose sum is σ = 30333524. Its totient is φ = 14000076.

The previous prime is 21000121. The next prime is 21000131. The reversal of 21000123 is 32100012.

It is a happy number.

It is not a de Polignac number, because 21000123 - 2¹ = 21000121 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2333347 = 21000123 / (2 + 1 + 0 + 0 + 0 + 1 + 2 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21000121) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166665 + ... + 1166682.

Almost surely, 2^21000123 is an apocalyptic number.

21000123 is a deficient number, since it is larger than the sum of its proper divisors (9333401).

21000123 is a wasteful number, since it uses less digits than its factorization.

21000123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2333353 (or 2333350 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 9.

The square root of 21000123 is about 4582.5891153364. The cubic root of 21000123 is about 275.8929562842.

Adding to 21000123 its reverse (32100012), we get a palindrome (53100135).

It can be divided in two parts, 2100012 and 3, that multiplied together give a palindrome (6300036).

The spelling of 21000123 in words is "twenty-one million, one hundred twenty-three", and thus it is an aban number.