991979 has 2 divisors, whose sum is σ = 991980. Its totient is φ = 991978.

The previous prime is 991973. The next prime is 991981. The reversal of 991979 is 979199.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991979 - 2⁸ = 991723 is a prime.

Together with 991981, it forms a pair of twin primes.

It is a Chen prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991979.

It is not a weakly prime, because it can be changed into another prime (991973) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495989 + 495990.

It is an arithmetic number, because the mean of its divisors is an integer number (495990).

2⁹⁹¹⁹⁷⁹ is an apocalyptic number.

991979 is a deficient number, since it is larger than the sum of its proper divisors (1).

991979 is an equidigital number, since it uses as much as digits as its factorization.

991979 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45927, while the sum is 44.

The square root of 991979 is about 995.9814255296. The cubic root of 991979 is about 99.7319152814.

The spelling of 991979 in words is "nine hundred ninety-one thousand, nine hundred seventy-nine".