21513521 has 8 divisors (see below), whose sum is σ = 21780264. Its totient is φ = 21248640.

The previous prime is 21513511. The next prime is 21513523. The reversal of 21513521 is 12531512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 215296 + 21298225 = 464^2 + 4615^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21513521 - 2¹⁴ = 21497137 is a prime.

It is a pancake number, because a pancake can be divided into 21513521 parts by 6559 straight cuts.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21513493 and 21513502.

It is not an unprimeable number, because it can be changed into a prime (21513523) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 50891 + ... + 51311.

It is an arithmetic number, because the mean of its divisors is an integer number (2722533).

Almost surely, 2^21513521 is an apocalyptic number.

It is an amenable number.

21513521 is a deficient number, since it is larger than the sum of its proper divisors (266743).

21513521 is a wasteful number, since it uses less digits than its factorization.

21513521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 931.

The product of its digits is 300, while the sum is 20.

The square root of 21513521 is about 4638.2670255172. The cubic root of 21513521 is about 278.1231662716.

Subtracting from 21513521 its reverse (12531512), we obtain a square (8982009 = 2997²).

The spelling of 21513521 in words is "twenty-one million, five hundred thirteen thousand, five hundred twenty-one".