991565 has 4 divisors (see below), whose sum is σ = 1189884. Its totient is φ = 793248.

The previous prime is 991547. The next prime is 991567. The reversal of 991565 is 565199.

991565 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: 565199 = 17 ⋅33247.

It can be written as a sum of positive squares in 2 ways, for example, as 537289 + 454276 = 733^2 + 674^2 .

It is a cyclic number.

It is not a de Polignac number, because 991565 - 2¹⁴ = 975181 is a prime.

It is a super-2 number, since 2×991565² = 1966402298450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991567) 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, 99152 + ... + 99161.

It is an arithmetic number, because the mean of its divisors is an integer number (297471).

2⁹⁹¹⁵⁶⁵ is an apocalyptic number.

It is an amenable number.

991565 is a deficient number, since it is larger than the sum of its proper divisors (198319).

991565 is a wasteful number, since it uses less digits than its factorization.

991565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 198318.

The product of its digits is 12150, while the sum is 35.

The square root of 991565 is about 995.7735686390. The cubic root of 991565 is about 99.7180390608.

The spelling of 991565 in words is "nine hundred ninety-one thousand, five hundred sixty-five".