21002123 has 4 divisors (see below), whose sum is σ = 22237560. Its totient is φ = 19766688.

The previous prime is 21002101. The next prime is 21002129. The reversal of 21002123 is 32120012.

It is a happy number.

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 21002123 - 2⁸ = 21001867 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21002129) 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, 617693 + ... + 617726.

It is an arithmetic number, because the mean of its divisors is an integer number (5559390).

Almost surely, 2^21002123 is an apocalyptic number.

21002123 is a deficient number, since it is larger than the sum of its proper divisors (1235437).

21002123 is a wasteful number, since it uses less digits than its factorization.

21002123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1235436.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21002123 is about 4582.8073273922. The cubic root of 21002123 is about 275.9017144614.

Adding to 21002123 its reverse (32120012), we get a palindrome (53122135).

The spelling of 21002123 in words is "twenty-one million, two thousand, one hundred twenty-three".