21201643 has 4 divisors (see below), whose sum is σ = 21601728. Its totient is φ = 20801560.

The previous prime is 21201641. The next prime is 21201647. The reversal of 21201643 is 34610212.

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 21201643 - 2¹ = 21201641 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21201643.

It is not an unprimeable number, because it can be changed into a prime (21201641) 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, 199963 + ... + 200068.

It is an arithmetic number, because the mean of its divisors is an integer number (5400432).

Almost surely, 2^21201643 is an apocalyptic number.

21201643 is a deficient number, since it is larger than the sum of its proper divisors (400085).

21201643 is an equidigital number, since it uses as much as digits as its factorization.

21201643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 400084.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21201643 is about 4604.5241882305. The cubic root of 21201643 is about 276.7726503196.

Adding to 21201643 its reverse (34610212), we get a palindrome (55811855).

The spelling of 21201643 in words is "twenty-one million, two hundred one thousand, six hundred forty-three".