21457643 has 4 divisors (see below), whose sum is σ = 22390608. Its totient is φ = 20524680.

The previous prime is 21457627. The next prime is 21457649. The reversal of 21457643 is 34675412.

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 21457643 - 2⁴ = 21457627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21457649) 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, 466448 + ... + 466493.

It is an arithmetic number, because the mean of its divisors is an integer number (5597652).

Almost surely, 2^21457643 is an apocalyptic number.

21457643 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21457643 is a deficient number, since it is larger than the sum of its proper divisors (932965).

21457643 is an equidigital number, since it uses as much as digits as its factorization.

21457643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 932964.

The product of its digits is 20160, while the sum is 32.

The square root of 21457643 is about 4632.2395231680. The cubic root of 21457643 is about 277.8821637131.

The spelling of 21457643 in words is "twenty-one million, four hundred fifty-seven thousand, six hundred forty-three".