21003643 has 4 divisors (see below), whose sum is σ = 21030048. Its totient is φ = 20977240.

The previous prime is 21003637. The next prime is 21003659. The reversal of 21003643 is 34630012.

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 21003643 - 2¹⁷ = 20872571 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 21003643.

It is not an unprimeable number, because it can be changed into a prime (21003673) 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, 11971 + ... + 13612.

It is an arithmetic number, because the mean of its divisors is an integer number (5257512).

Almost surely, 2^21003643 is an apocalyptic number.

21003643 is a deficient number, since it is larger than the sum of its proper divisors (26405).

21003643 is an equidigital number, since it uses as much as digits as its factorization.

21003643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26404.

The product of its (nonzero) digits is 432, while the sum is 19.

The square root of 21003643 is about 4582.9731616059. The cubic root of 21003643 is about 275.9083703042.

Adding to 21003643 its reverse (34630012), we get a palindrome (55633655).

The spelling of 21003643 in words is "twenty-one million, three thousand, six hundred forty-three".