815561 has 4 divisors (see below), whose sum is σ = 821652. Its totient is φ = 809472.

The previous prime is 815543. The next prime is 815569. The reversal of 815561 is 165518.

815561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165518 = 2 ⋅82759.

It can be written as a sum of positive squares in 2 ways, for example, as 175561 + 640000 = 419^2 + 800^2 .

It is a cyclic number.

It is not a de Polignac number, because 815561 - 2¹⁰ = 814537 is a prime.

It is a Duffinian number.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 815561.

It is not an unprimeable number, because it can be changed into a prime (815569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2840 + ... + 3113.

It is an arithmetic number, because the mean of its divisors is an integer number (205413).

2⁸¹⁵⁵⁶¹ is an apocalyptic number.

It is an amenable number.

815561 is a deficient number, since it is larger than the sum of its proper divisors (6091).

815561 is a wasteful number, since it uses less digits than its factorization.

815561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6090.

The product of its digits is 1200, while the sum is 26.

The square root of 815561 is about 903.0841599762. The cubic root of 815561 is about 93.4298137807.

The spelling of 815561 in words is "eight hundred fifteen thousand, five hundred sixty-one".