21015521 has 8 divisors (see below), whose sum is σ = 21258624. Its totient is φ = 20774160.

The previous prime is 21015497. The next prime is 21015523. The reversal of 21015521 is 12551012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21015521 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21015521.

It is not an unprimeable number, because it can be changed into a prime (21015523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 57080 + ... + 57446.

It is an arithmetic number, because the mean of its divisors is an integer number (2657328).

Almost surely, 2^21015521 is an apocalyptic number.

It is an amenable number.

21015521 is a deficient number, since it is larger than the sum of its proper divisors (243103).

21015521 is a wasteful number, since it uses less digits than its factorization.

21015521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 871.

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21015521 is about 4584.2688620979. The cubic root of 21015521 is about 275.9603711569.

Adding to 21015521 its reverse (12551012), we get a palindrome (33566533).

The spelling of 21015521 in words is "twenty-one million, fifteen thousand, five hundred twenty-one".