991031 has 2 divisors, whose sum is σ = 991032. Its totient is φ = 991030.

The previous prime is 991027. The next prime is 991037. The reversal of 991031 is 130199.

It is a weak prime.

It is an emirp because it is prime and its reverse (130199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991031 - 2² = 991027 is a prime.

It is a super-2 number, since 2×991031² = 1964284885922, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 990988 and 991006.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991037) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495515 + 495516.

It is an arithmetic number, because the mean of its divisors is an integer number (495516).

2⁹⁹¹⁰³¹ is an apocalyptic number.

991031 is a deficient number, since it is larger than the sum of its proper divisors (1).

991031 is an equidigital number, since it uses as much as digits as its factorization.

991031 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 243, while the sum is 23.

The square root of 991031 is about 995.5053992822. The cubic root of 991031 is about 99.7001350422.

The spelling of 991031 in words is "nine hundred ninety-one thousand, thirty-one".