21123253121 has 4 divisors (see below), whose sum is σ = 21694151892. Its totient is φ = 20552354352.

The previous prime is 21123253111. The next prime is 21123253127. The reversal of 21123253121 is 12135232112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 19988304400 + 1134948721 = 141380^2 + 33689^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123253121 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21123253127) 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, 285449330 + ... + 285449403.

It is an arithmetic number, because the mean of its divisors is an integer number (5423537973).

Almost surely, 2^21123253121 is an apocalyptic number.

It is an amenable number.

21123253121 is a deficient number, since it is larger than the sum of its proper divisors (570898771).

21123253121 is an equidigital number, since it uses as much as digits as its factorization.

21123253121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570898770.

The product of its digits is 720, while the sum is 23.

Adding to 21123253121 its reverse (12135232112), we get a palindrome (33258485233).

The spelling of 21123253121 in words is "twenty-one billion, one hundred twenty-three million, two hundred fifty-three thousand, one hundred twenty-one".