981991 has 8 divisors (see below), whose sum is σ = 1031184. Its totient is φ = 934080.

The previous prime is 981983. The next prime is 982021. The reversal of 981991 is 199189.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 981991 - 2³ = 981983 is a prime.

It is a Duffinian number.

981991 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 981991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (981941) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1485 + ... + 2041.

It is an arithmetic number, because the mean of its divisors is an integer number (128898).

2⁹⁸¹⁹⁹¹ is an apocalyptic number.

981991 is a deficient number, since it is larger than the sum of its proper divisors (49193).

981991 is a wasteful number, since it uses less digits than its factorization.

981991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 641.

The product of its digits is 5832, while the sum is 37.

The square root of 981991 is about 990.9545902815. The cubic root of 981991 is about 99.3960599064.

The spelling of 981991 in words is "nine hundred eighty-one thousand, nine hundred ninety-one".