21388643 has 4 divisors (see below), whose sum is σ = 22318608. Its totient is φ = 20458680.

The previous prime is 21388639. The next prime is 21388649. The reversal of 21388643 is 34688312.

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 21388643 - 2² = 21388639 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21388649) 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, 464948 + ... + 464993.

It is an arithmetic number, because the mean of its divisors is an integer number (5579652).

Almost surely, 2^21388643 is an apocalyptic number.

21388643 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21388643 is a deficient number, since it is larger than the sum of its proper divisors (929965).

21388643 is an equidigital number, since it uses as much as digits as its factorization.

21388643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 929964.

The product of its digits is 27648, while the sum is 35.

The square root of 21388643 is about 4624.7857247661. The cubic root of 21388643 is about 277.5839877802.

The spelling of 21388643 in words is "twenty-one million, three hundred eighty-eight thousand, six hundred forty-three".