991786 has 4 divisors (see below), whose sum is σ = 1487682. Its totient is φ = 495892.

The previous prime is 991777. The next prime is 991811. The reversal of 991786 is 687199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 687199 = 521 ⋅1319.

It can be written as a sum of positive squares in only one way, i.e., 855625 + 136161 = 925^2 + 369^2 .

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

991786 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 247945 + ... + 247948.

2⁹⁹¹⁷⁸⁶ is an apocalyptic number.

991786 is a deficient number, since it is larger than the sum of its proper divisors (495896).

991786 is a wasteful number, since it uses less digits than its factorization.

991786 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 495895.

The product of its digits is 27216, while the sum is 40.

The square root of 991786 is about 995.8845314593. The cubic root of 991786 is about 99.7254468958.

The spelling of 991786 in words is "nine hundred ninety-one thousand, seven hundred eighty-six".