991777 has 2 divisors, whose sum is σ = 991778. Its totient is φ = 991776.

The previous prime is 991751. The next prime is 991811. The reversal of 991777 is 777199.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 913936 + 77841 = 956^2 + 279^2 .

It is an emirp because it is prime and its reverse (777199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991777 - 2¹⁵ = 959009 is a prime.

991777 is a lucky number.

It is a nialpdrome in base 16.

It is not a weakly prime, because it can be changed into another prime (991717) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495888 + 495889.

It is an arithmetic number, because the mean of its divisors is an integer number (495889).

2⁹⁹¹⁷⁷⁷ is an apocalyptic number.

It is an amenable number.

991777 is a deficient number, since it is larger than the sum of its proper divisors (1).

991777 is an equidigital number, since it uses as much as digits as its factorization.

991777 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27783, while the sum is 40.

The square root of 991777 is about 995.8800128530. The cubic root of 991777 is about 99.7251452407.

The spelling of 991777 in words is "nine hundred ninety-one thousand, seven hundred seventy-seven".