21259643 has 4 divisors (see below), whose sum is σ = 21296088. Its totient is φ = 21223200.

The previous prime is 21259627. The next prime is 21259657. The reversal of 21259643 is 34695212.

It is a happy number.

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 21259643 - 2⁴ = 21259627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21259603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17333 + ... + 18518.

It is an arithmetic number, because the mean of its divisors is an integer number (5324022).

Almost surely, 2^21259643 is an apocalyptic number.

21259643 is a deficient number, since it is larger than the sum of its proper divisors (36445).

21259643 is an equidigital number, since it uses as much as digits as its factorization.

21259643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36444.

The product of its digits is 12960, while the sum is 32.

The square root of 21259643 is about 4610.8180402180. The cubic root of 21259643 is about 277.0248036976.

The spelling of 21259643 in words is "twenty-one million, two hundred fifty-nine thousand, six hundred forty-three".