21123253421 has 4 divisors (see below), whose sum is σ = 21851641500. Its totient is φ = 20394865344.

The previous prime is 21123253387. The next prime is 21123253427. The reversal of 21123253421 is 12435232112.

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 9606744196 + 11516509225 = 98014^2 + 107315^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123253421 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123253427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 364193996 + ... + 364194053.

It is an arithmetic number, because the mean of its divisors is an integer number (5462910375).

Almost surely, 2^21123253421 is an apocalyptic number.

It is an amenable number.

21123253421 is a deficient number, since it is larger than the sum of its proper divisors (728388079).

21123253421 is an equidigital number, since it uses as much as digits as its factorization.

21123253421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 728388078.

The product of its digits is 2880, while the sum is 26.

Adding to 21123253421 its reverse (12435232112), we get a palindrome (33558485533).

The spelling of 21123253421 in words is "twenty-one billion, one hundred twenty-three million, two hundred fifty-three thousand, four hundred twenty-one".