21043643 has 4 divisors (see below), whose sum is σ = 21958608. Its totient is φ = 20128680.

The previous prime is 21043613. The next prime is 21043661. The reversal of 21043643 is 34634012.

It is a happy number.

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

It is not a de Polignac number, because 21043643 - 2⁶ = 21043579 is a prime.

It is a super-2 number, since 2×21043643² = 885669821422898, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 914941 = 21043643 / (2 + 1 + 0 + 4 + 3 + 6 + 4 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21043613) 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, 457448 + ... + 457493.

It is an arithmetic number, because the mean of its divisors is an integer number (5489652).

Almost surely, 2^21043643 is an apocalyptic number.

21043643 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21043643 is a deficient number, since it is larger than the sum of its proper divisors (914965).

21043643 is an equidigital number, since it uses as much as digits as its factorization.

21043643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 914964.

The product of its (nonzero) digits is 1728, while the sum is 23.

The square root of 21043643 is about 4587.3350651549. The cubic root of 21043643 is about 276.0834087683.

Adding to 21043643 its reverse (34634012), we get a palindrome (55677655).

The spelling of 21043643 in words is "twenty-one million, forty-three thousand, six hundred forty-three".