815665861 has 4 divisors (see below), whose sum is σ = 843792300. Its totient is φ = 787539424.

The previous prime is 815665847. The next prime is 815665891. The reversal of 815665861 is 168566518.

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 350400961 + 465264900 = 18719^2 + 21570^2 .

It is a cyclic number.

It is not a de Polignac number, because 815665861 - 2⁷ = 815665733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (815665841) 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 3 ways as a sum of consecutive naturals, for example, 14063176 + ... + 14063233.

It is an arithmetic number, because the mean of its divisors is an integer number (210948075).

Almost surely, 2^815665861 is an apocalyptic number.

It is an amenable number.

815665861 is a deficient number, since it is larger than the sum of its proper divisors (28126439).

815665861 is a wasteful number, since it uses less digits than its factorization.

815665861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28126438.

The product of its digits is 345600, while the sum is 46.

The square root of 815665861 is about 28559.8645129840. The cubic root of 815665861 is about 934.3381786454.

The spelling of 815665861 in words is "eight hundred fifteen million, six hundred sixty-five thousand, eight hundred sixty-one".