21311660521 has 4 divisors (see below), whose sum is σ = 21378890052. Its totient is φ = 21244430992.

The previous prime is 21311660519. The next prime is 21311660527. The reversal of 21311660521 is 12506611312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11812429225 + 9499231296 = 108685^2 + 97464^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311660521 - 2¹ = 21311660519 is a prime.

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 21311660521.

It is not an unprimeable number, because it can be changed into a prime (21311660527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33614290 + ... + 33614923.

It is an arithmetic number, because the mean of its divisors is an integer number (5344722513).

Almost surely, 2^21311660521 is an apocalyptic number.

It is an amenable number.

21311660521 is a deficient number, since it is larger than the sum of its proper divisors (67229531).

21311660521 is an equidigital number, since it uses as much as digits as its factorization.

21311660521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67229530.

The product of its (nonzero) digits is 2160, while the sum is 28.

The spelling of 21311660521 in words is "twenty-one billion, three hundred eleven million, six hundred sixty thousand, five hundred twenty-one".