991591243 has 2 divisors, whose sum is σ = 991591244. Its totient is φ = 991591242.

The previous prime is 991591201. The next prime is 991591253. The reversal of 991591243 is 342195199.

It is a strong prime.

It is an emirp because it is prime and its reverse (342195199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991591243 - 2⁹ = 991590731 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991591243.

It is not a weakly prime, because it can be changed into another prime (991591253) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495795621 + 495795622.

It is an arithmetic number, because the mean of its divisors is an integer number (495795622).

Almost surely, 2^991591243 is an apocalyptic number.

991591243 is a deficient number, since it is larger than the sum of its proper divisors (1).

991591243 is an equidigital number, since it uses as much as digits as its factorization.

991591243 is an evil number, because the sum of its binary digits is even.

The product of its digits is 87480, while the sum is 43.

The square root of 991591243 is about 31489.5418035893. The cubic root of 991591243 is about 997.1891877369.

The spelling of 991591243 in words is "nine hundred ninety-one million, five hundred ninety-one thousand, two hundred forty-three".