21518507521 has 8 divisors (see below), whose sum is σ = 24597143424. Its totient is φ = 18441012480.

The previous prime is 21518507497. The next prime is 21518507531. The reversal of 21518507521 is 12570581512.

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 21518507521 - 2⁹ = 21518507009 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21518507531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 244405 + ... + 320578.

It is an arithmetic number, because the mean of its divisors is an integer number (3074642928).

Almost surely, 2^21518507521 is an apocalyptic number.

It is an amenable number.

21518507521 is a deficient number, since it is larger than the sum of its proper divisors (3078635903).

21518507521 is an equidigital number, since it uses as much as digits as its factorization.

21518507521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 570431.

The product of its (nonzero) digits is 28000, while the sum is 37.

The spelling of 21518507521 in words is "twenty-one billion, five hundred eighteen million, five hundred seven thousand, five hundred twenty-one".