21643943 has 4 divisors (see below), whose sum is σ = 22585008. Its totient is φ = 20702880.

The previous prime is 21643939. The next prime is 21643961. The reversal of 21643943 is 34934612.

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 21643943 - 2² = 21643939 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 (21643913) 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, 470498 + ... + 470543.

It is an arithmetic number, because the mean of its divisors is an integer number (5646252).

Almost surely, 2^21643943 is an apocalyptic number.

21643943 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21643943 is a deficient number, since it is larger than the sum of its proper divisors (941065).

21643943 is an equidigital number, since it uses as much as digits as its factorization.

21643943 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 941064.

The product of its digits is 15552, while the sum is 32.

The square root of 21643943 is about 4652.3051275685. The cubic root of 21643943 is about 278.6840588859.

The spelling of 21643943 in words is "twenty-one million, six hundred forty-three thousand, nine hundred forty-three".