21043521 has 6 divisors (see below), whose sum is σ = 30396210. Its totient is φ = 14029008.

The previous prime is 21043499. The next prime is 21043523. The reversal of 21043521 is 12534012.

21043521 is a `hidden beast` number, since 210 + 435 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 20930625 + 112896 = 4575^2 + 336^2 .

It is not a de Polignac number, because 21043521 - 2⁵ = 21043489 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21043494 and 21043503.

It is not an unprimeable number, because it can be changed into a prime (21043523) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1169076 + ... + 1169093.

It is an arithmetic number, because the mean of its divisors is an integer number (5066035).

Almost surely, 2^21043521 is an apocalyptic number.

It is an amenable number.

21043521 is a deficient number, since it is larger than the sum of its proper divisors (9352689).

21043521 is a wasteful number, since it uses less digits than its factorization.

21043521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2338175 (or 2338172 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21043521 is about 4587.3217676548. The cubic root of 21043521 is about 276.0828752384.

Adding to 21043521 its reverse (12534012), we get a palindrome (33577533).

It can be divided in two parts, 2104 and 3521, that added together give a square (5625 = 75²).

The spelling of 21043521 in words is "twenty-one million, forty-three thousand, five hundred twenty-one".