21051521 has 8 divisors (see below), whose sum is σ = 21436320. Its totient is φ = 20669472.

The previous prime is 21051493. The next prime is 21051523. The reversal of 21051521 is 12515012.

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-21051521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21051521.

It is not an unprimeable number, because it can be changed into a prime (21051523) 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, 20150 + ... + 21168.

It is an arithmetic number, because the mean of its divisors is an integer number (2679540).

Almost surely, 2^21051521 is an apocalyptic number.

It is an amenable number.

21051521 is a deficient number, since it is larger than the sum of its proper divisors (384799).

21051521 is a wasteful number, since it uses less digits than its factorization.

21051521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1375.

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

The square root of 21051521 is about 4588.1936532801. The cubic root of 21051521 is about 276.1178564435.

Adding to 21051521 its reverse (12515012), we get a palindrome (33566533).

The spelling of 21051521 in words is "twenty-one million, fifty-one thousand, five hundred twenty-one".