21307521 has 8 divisors (see below), whose sum is σ = 28459264. Its totient is φ = 14180400.

The previous prime is 21307519. The next prime is 21307529. The reversal of 21307521 is 12570312.

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

It is not a de Polignac number, because 21307521 - 2¹ = 21307519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21307529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4030 + ... + 7671.

It is an arithmetic number, because the mean of its divisors is an integer number (3557408).

Almost surely, 2^21307521 is an apocalyptic number.

It is an amenable number.

21307521 is a deficient number, since it is larger than the sum of its proper divisors (7151743).

21307521 is a wasteful number, since it uses less digits than its factorization.

21307521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12311.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21307521 is about 4616.0070407225. The cubic root of 21307521 is about 277.2326066435.

Adding to 21307521 its reverse (12570312), we get a palindrome (33877833).

The spelling of 21307521 in words is "twenty-one million, three hundred seven thousand, five hundred twenty-one".