21508521 has 8 divisors (see below), whose sum is σ = 28761600. Its totient is φ = 14297232.

The previous prime is 21508493. The next prime is 21508523. The reversal of 21508521 is 12580512.

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

It is not a de Polignac number, because 21508521 - 2¹¹ = 21506473 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21508491 and 21508500.

It is not an unprimeable number, because it can be changed into a prime (21508523) 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, 9225 + ... + 11318.

It is an arithmetic number, because the mean of its divisors is an integer number (3595200).

Almost surely, 2^21508521 is an apocalyptic number.

It is an amenable number.

21508521 is a deficient number, since it is larger than the sum of its proper divisors (7253079).

21508521 is a wasteful number, since it uses less digits than its factorization.

21508521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20895.

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 21508521 is about 4637.7279997861. The cubic root of 21508521 is about 278.1016182170.

The spelling of 21508521 in words is "twenty-one million, five hundred eight thousand, five hundred twenty-one".