21518680521 has 8 divisors (see below), whose sum is σ = 30898618240. Its totient is φ = 13242264912.

The previous prime is 21518680511. The next prime is 21518680537. The reversal of 21518680521 is 12508681512.

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

It is not a de Polignac number, because 21518680521 - 2⁶ = 21518680457 is a prime.

It is a super-2 number, since 2×21518680521² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (39), and also a Moran number because the ratio is a prime number: 551761039 = 21518680521 / (2 + 1 + 5 + 1 + 8 + 6 + 8 + 0 + 5 + 2 + 1).

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 21518680521.

It is not an unprimeable number, because it can be changed into a prime (21518680501) 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, 275880481 + ... + 275880558.

It is an arithmetic number, because the mean of its divisors is an integer number (3862327280).

Almost surely, 2^21518680521 is an apocalyptic number.

It is an amenable number.

21518680521 is a deficient number, since it is larger than the sum of its proper divisors (9379937719).

21518680521 is a wasteful number, since it uses less digits than its factorization.

21518680521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 551761055.

The product of its (nonzero) digits is 38400, while the sum is 39.

Subtracting from 21518680521 its reverse (12508681512), we obtain a palindrome (9009999009).

The spelling of 21518680521 in words is "twenty-one billion, five hundred eighteen million, six hundred eighty thousand, five hundred twenty-one".