21397643 has 4 divisors (see below), whose sum is σ = 21852960. Its totient is φ = 20942328.

The previous prime is 21397633. The next prime is 21397669. The reversal of 21397643 is 34679312.

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 21397643 - 2¹⁴ = 21381259 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21397603) 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, 227588 + ... + 227681.

It is an arithmetic number, because the mean of its divisors is an integer number (5463240).

Almost surely, 2^21397643 is an apocalyptic number.

21397643 is a deficient number, since it is larger than the sum of its proper divisors (455317).

21397643 is an equidigital number, since it uses as much as digits as its factorization.

21397643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 455316.

The product of its digits is 27216, while the sum is 35.

The square root of 21397643 is about 4625.7586404827. The cubic root of 21397643 is about 277.6229166261.

The spelling of 21397643 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred forty-three".