21668943 has 4 divisors (see below), whose sum is σ = 28891928. Its totient is φ = 14445960.

The previous prime is 21668929. The next prime is 21668957. The reversal of 21668943 is 34986612.

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

It is an interprime number because it is at equal distance from previous prime (21668929) and next prime (21668957).

It is not a de Polignac number, because 21668943 - 2¹⁷ = 21537871 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 (21668923) 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, 3611488 + ... + 3611493.

It is an arithmetic number, because the mean of its divisors is an integer number (7222982).

Almost surely, 2^21668943 is an apocalyptic number.

21668943 is a deficient number, since it is larger than the sum of its proper divisors (7222985).

21668943 is an equidigital number, since it uses as much as digits as its factorization.

21668943 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7222984.

The product of its digits is 62208, while the sum is 39.

The square root of 21668943 is about 4654.9911922580. The cubic root of 21668943 is about 278.7913163101.

The spelling of 21668943 in words is "twenty-one million, six hundred sixty-eight thousand, nine hundred forty-three".