813991 has 2 divisors, whose sum is σ = 813992. Its totient is φ = 813990.

The previous prime is 813971. The next prime is 813997. The reversal of 813991 is 199318.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 813991 - 2⁷ = 813863 is a prime.

It is a plaindrome in base 13.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (813997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 406995 + 406996.

It is an arithmetic number, because the mean of its divisors is an integer number (406996).

2⁸¹³⁹⁹¹ is an apocalyptic number.

813991 is a deficient number, since it is larger than the sum of its proper divisors (1).

813991 is an equidigital number, since it uses as much as digits as its factorization.

813991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1944, while the sum is 31.

The square root of 813991 is about 902.2144977776. The cubic root of 813991 is about 93.3698227505.

The spelling of 813991 in words is "eight hundred thirteen thousand, nine hundred ninety-one".