21156543 has 12 divisors (see below), whose sum is σ = 30643080. Its totient is φ = 14065776.

The previous prime is 21156529. The next prime is 21156589. The reversal of 21156543 is 34565112.

21156543 is a `hidden beast` number, since 2 + 1 + 1 + 5 + 654 + 3 = 666.

It is not a de Polignac number, because 21156543 - 2⁵ = 21156511 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21156743) 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, 480 + ... + 6522.

It is an arithmetic number, because the mean of its divisors is an integer number (2553590).

Almost surely, 2^21156543 is an apocalyptic number.

21156543 is a deficient number, since it is larger than the sum of its proper divisors (9486537).

21156543 is a wasteful number, since it uses less digits than its factorization.

21156543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6438 (or 6435 counting only the distinct ones).

The product of its digits is 3600, while the sum is 27.

The square root of 21156543 is about 4599.6242237818. The cubic root of 21156543 is about 276.5762613281.

The spelling of 21156543 in words is "twenty-one million, one hundred fifty-six thousand, five hundred forty-three".