21521042423 has 4 divisors (see below), whose sum is σ = 21525069648. Its totient is φ = 21517015200.

The previous prime is 21521042401. The next prime is 21521042453. The reversal of 21521042423 is 32424012512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21521042423 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21521042392 and 21521042401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521042453) 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, 2005586 + ... + 2016287.

It is an arithmetic number, because the mean of its divisors is an integer number (5381267412).

Almost surely, 2^21521042423 is an apocalyptic number.

21521042423 is a deficient number, since it is larger than the sum of its proper divisors (4027225).

21521042423 is an equidigital number, since it uses as much as digits as its factorization.

21521042423 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4027224.

The product of its (nonzero) digits is 3840, while the sum is 26.

Adding to 21521042423 its reverse (32424012512), we get a palindrome (53945054935).

The spelling of 21521042423 in words is "twenty-one billion, five hundred twenty-one million, forty-two thousand, four hundred twenty-three".