21312543 has 16 divisors (see below), whose sum is σ = 34387200. Its totient is φ = 11462016.

The previous prime is 21312539. The next prime is 21312587. The reversal of 21312543 is 34521312.

It is not a de Polignac number, because 21312543 - 2² = 21312539 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312523) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 29493 + ... + 30206.

It is an arithmetic number, because the mean of its divisors is an integer number (2149200).

Almost surely, 2^21312543 is an apocalyptic number.

21312543 is a deficient number, since it is larger than the sum of its proper divisors (13074657).

21312543 is a wasteful number, since it uses less digits than its factorization.

21312543 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59726.

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

The square root of 21312543 is about 4616.5509853136. The cubic root of 21312543 is about 277.2543853820.

Adding to 21312543 its reverse (34521312), we get a palindrome (55833855).

The spelling of 21312543 in words is "twenty-one million, three hundred twelve thousand, five hundred forty-three".