16566521521 has 9 divisors (see below), whose sum is σ = 18211038699. Its totient is φ = 15059187000.

The previous prime is 16566521509. The next prime is 16566521537. The reversal of 16566521521 is 12512566561.

The square root of 16566521521 is 128711.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 12959317921 + 3607203600 = 113839^2 + 60060^2 .

It is not a de Polignac number, because 16566521521 - 2⁷ = 16566521393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16566521501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1409971 + ... + 1421671.

Almost surely, 2^16566521521 is an apocalyptic number.

16566521521 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

16566521521 is the 128711-st square number.

16566521521 is the 64356-th centered octagonal number.

It is an amenable number.

16566521521 is a deficient number, since it is larger than the sum of its proper divisors (1644517178).

16566521521 is an frugal number, since it uses more digits than its factorization.

16566521521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23424 (or 11712 counting only the distinct ones).

The product of its digits is 108000, while the sum is 40.

The spelling of 16566521521 in words is "sixteen billion, five hundred sixty-six million, five hundred twenty-one thousand, five hundred twenty-one".