840991 has 2 divisors, whose sum is σ = 840992. Its totient is φ = 840990.

The previous prime is 840989. The next prime is 841003. The reversal of 840991 is 199048.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 840991 - 2¹ = 840989 is a prime.

Together with 840989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (840911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 420495 + 420496.

It is an arithmetic number, because the mean of its divisors is an integer number (420496).

2⁸⁴⁰⁹⁹¹ is an apocalyptic number.

840991 is a deficient number, since it is larger than the sum of its proper divisors (1).

840991 is an equidigital number, since it uses as much as digits as its factorization.

840991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2592, while the sum is 31.

The square root of 840991 is about 917.0556144531. The cubic root of 840991 is about 94.3909700618.

It can be divided in two parts, 84099 and 1, that added together give a square (84100 = 290²).

The spelling of 840991 in words is "eight hundred forty thousand, nine hundred ninety-one".