21973539 has 16 divisors (see below), whose sum is σ = 33600512. Its totient is φ = 12512448.

The previous prime is 21973529. The next prime is 21973591. The reversal of 21973539 is 93537912.

It is not a de Polignac number, because 21973539 - 2¹⁹ = 21449251 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21973497 and 21973506.

It is not an unprimeable number, because it can be changed into a prime (21973529) 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, 4902 + ... + 8244.

It is an arithmetic number, because the mean of its divisors is an integer number (2100032).

Almost surely, 2^21973539 is an apocalyptic number.

21973539 is a deficient number, since it is larger than the sum of its proper divisors (11626973).

21973539 is a wasteful number, since it uses less digits than its factorization.

21973539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3666.

The product of its digits is 51030, while the sum is 39.

The square root of 21973539 is about 4687.5941590543. The cubic root of 21973539 is about 280.0915474458.

The spelling of 21973539 in words is "twenty-one million, nine hundred seventy-three thousand, five hundred thirty-nine".