21756539 has 12 divisors (see below), whose sum is σ = 26641800. Its totient is φ = 17666208.

The previous prime is 21756529. The next prime is 21756547. The reversal of 21756539 is 93565712.

It is a happy number.

It is not a de Polignac number, because 21756539 - 2⁸ = 21756283 is a prime.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21756529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10754 + ... + 12615.

It is an arithmetic number, because the mean of its divisors is an integer number (2220150).

Almost surely, 2^21756539 is an apocalyptic number.

21756539 is a deficient number, since it is larger than the sum of its proper divisors (4885261).

21756539 is a wasteful number, since it uses less digits than its factorization.

21756539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23402 (or 23395 counting only the distinct ones).

The product of its digits is 56700, while the sum is 38.

The square root of 21756539 is about 4664.3905282470. The cubic root of 21756539 is about 279.1664795227.

The spelling of 21756539 in words is "twenty-one million, seven hundred fifty-six thousand, five hundred thirty-nine".