21002543 has 4 divisors (see below), whose sum is σ = 22107960. Its totient is φ = 19897128.

The previous prime is 21002539. The next prime is 21002549. The reversal of 21002543 is 34520012.

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 21002543 - 2² = 21002539 is a prime.

It is a super-2 number, since 2×21002543² = 882213624933698, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002549) 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, 552680 + ... + 552717.

It is an arithmetic number, because the mean of its divisors is an integer number (5526990).

Almost surely, 2^21002543 is an apocalyptic number.

21002543 is a deficient number, since it is larger than the sum of its proper divisors (1105417).

21002543 is a wasteful number, since it uses less digits than its factorization.

21002543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1105416.

The product of its (nonzero) digits is 240, while the sum is 17.

The square root of 21002543 is about 4582.8531506039. The cubic root of 21002543 is about 275.9035536080.

Adding to 21002543 its reverse (34520012), we get a palindrome (55522555).

The spelling of 21002543 in words is "twenty-one million, two thousand, five hundred forty-three".