815888561 has 4 divisors (see below), whose sum is σ = 835788324. Its totient is φ = 795988800.

The previous prime is 815888551. The next prime is 815888569. The reversal of 815888561 is 165888518.

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 357928561 + 457960000 = 18919^2 + 21400^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-815888561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (815888569) 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, 9949820 + ... + 9949901.

It is an arithmetic number, because the mean of its divisors is an integer number (208947081).

Almost surely, 2^815888561 is an apocalyptic number.

It is an amenable number.

815888561 is a deficient number, since it is larger than the sum of its proper divisors (19899763).

815888561 is a wasteful number, since it uses less digits than its factorization.

815888561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19899762.

The product of its digits is 614400, while the sum is 50.

The square root of 815888561 is about 28563.7630749171. The cubic root of 815888561 is about 934.4232045480.

The spelling of 815888561 in words is "eight hundred fifteen million, eight hundred eighty-eight thousand, five hundred sixty-one".