21205123 has 2 divisors, whose sum is σ = 21205124. Its totient is φ = 21205122.

The previous prime is 21205111. The next prime is 21205127. The reversal of 21205123 is 32150212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21205123 - 2¹⁷ = 21074051 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21205097 and 21205106.

It is not a weakly prime, because it can be changed into another prime (21205127) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602561 + 10602562.

It is an arithmetic number, because the mean of its divisors is an integer number (10602562).

Almost surely, 2^21205123 is an apocalyptic number.

21205123 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205123 is an equidigital number, since it uses as much as digits as its factorization.

21205123 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21205123 is about 4604.9020619336. The cubic root of 21205123 is about 276.7877924815.

Adding to 21205123 its reverse (32150212), we get a palindrome (53355335).

The spelling of 21205123 in words is "twenty-one million, two hundred five thousand, one hundred twenty-three".