8665561921 has 3 divisors (see below), whose sum is σ = 8665655011. Its totient is φ = 8665468832.

The previous prime is 8665561897. The next prime is 8665561939. The reversal of 8665561921 is 1291655668.

The square root of 8665561921 is 93089.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 8641747521 + 23814400 = 92961^2 + 4880^2 .

It is a de Polignac number, because none of the positive numbers 2^k-8665561921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (8665561951) 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 2 ways as a sum of consecutive naturals, for example, 46545 + ... + 139633.

Almost surely, 2^8665561921 is an apocalyptic number.

8665561921 is the 93089-th square number.

8665561921 is the 46545-th centered octagonal number.

It is an amenable number.

8665561921 is a deficient number, since it is larger than the sum of its proper divisors (93090).

8665561921 is an frugal number, since it uses more digits than its factorization.

8665561921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 186178 (or 93089 counting only the distinct ones).

The product of its digits is 777600, while the sum is 49.

The cubic root of 8665561921 is about 2053.9927672320.

Multiplying 8665561921 by its sum of digits (49), we get a square (424612534129 = 651623²).

The spelling of 8665561921 in words is "eight billion, six hundred sixty-five million, five hundred sixty-one thousand, nine hundred twenty-one".