21643423 has 4 divisors (see below), whose sum is σ = 21713328. Its totient is φ = 21573520.

The previous prime is 21643421. The next prime is 21643429. The reversal of 21643423 is 32434612.

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 21643423 - 2¹ = 21643421 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 (21643421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 34486 + ... + 35107.

It is an arithmetic number, because the mean of its divisors is an integer number (5428332).

Almost surely, 2^21643423 is an apocalyptic number.

21643423 is a deficient number, since it is larger than the sum of its proper divisors (69905).

21643423 is an equidigital number, since it uses as much as digits as its factorization.

21643423 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69904.

The product of its digits is 3456, while the sum is 25.

The square root of 21643423 is about 4652.2492409586. The cubic root of 21643423 is about 278.6818270549.

The spelling of 21643423 in words is "twenty-one million, six hundred forty-three thousand, four hundred twenty-three".