21305643 has 8 divisors (see below), whose sum is σ = 28535808. Its totient is φ = 14139624.

The previous prime is 21305639. The next prime is 21305651. The reversal of 21305643 is 34650312.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21305643 - 2² = 21305639 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21305663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15255 + ... + 16592.

It is an arithmetic number, because the mean of its divisors is an integer number (3566976).

Almost surely, 2^21305643 is an apocalyptic number.

21305643 is a deficient number, since it is larger than the sum of its proper divisors (7230165).

21305643 is a wasteful number, since it uses less digits than its factorization.

21305643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32073.

The product of its (nonzero) digits is 2160, while the sum is 24.

The square root of 21305643 is about 4615.8036136734. The cubic root of 21305643 is about 277.2244615050.

Adding to 21305643 its reverse (34650312), we get a palindrome (55955955).

The spelling of 21305643 in words is "twenty-one million, three hundred five thousand, six hundred forty-three".