991851 has 16 divisors (see below), whose sum is σ = 1534464. Its totient is φ = 558144.

The previous prime is 991817. The next prime is 991867. The reversal of 991851 is 158199.

It is not a de Polignac number, because 991851 - 2⁷ = 991723 is a prime.

It is not an unprimeable number, because it can be changed into a prime (991811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1210 + ... + 1856.

It is an arithmetic number, because the mean of its divisors is an integer number (95904).

2⁹⁹¹⁸⁵¹ is an apocalyptic number.

991851 is a deficient number, since it is larger than the sum of its proper divisors (542613).

991851 is a wasteful number, since it uses less digits than its factorization.

991851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 730.

The product of its digits is 3240, while the sum is 33.

The square root of 991851 is about 995.9171652301. The cubic root of 991851 is about 99.7276254613.

The spelling of 991851 in words is "nine hundred ninety-one thousand, eight hundred fifty-one".