21006543 has 12 divisors (see below), whose sum is σ = 29754440. Its totient is φ = 13180032.

The previous prime is 21006523. The next prime is 21006547. The reversal of 21006543 is 34560012.

It is a happy number.

It is not a de Polignac number, because 21006543 - 2⁵ = 21006511 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006547) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11248 + ... + 12981.

Almost surely, 2^21006543 is an apocalyptic number.

21006543 is a deficient number, since it is larger than the sum of its proper divisors (8747897).

21006543 is a wasteful number, since it uses less digits than its factorization.

21006543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24266 (or 24249 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 21.

The square root of 21006543 is about 4583.2895391847. The cubic root of 21006543 is about 275.9210680610.

Adding to 21006543 its reverse (34560012), we get a palindrome (55566555).

The spelling of 21006543 in words is "twenty-one million, six thousand, five hundred forty-three".