1991871 has 24 divisors (see below), whose sum is σ = 3412864. Its totient is φ = 1137240.

The previous prime is 1991863. The next prime is 1991879. The reversal of 1991871 is 1781991.

It is an interprime number because it is at equal distance from previous prime (1991863) and next prime (1991879).

It is not a de Polignac number, because 1991871 - 2³ = 1991863 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991879) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1116 + ... + 2286.

2^1991871 is an apocalyptic number.

1991871 is a deficient number, since it is larger than the sum of its proper divisors (1420993).

1991871 is an equidigital number, since it uses as much as digits as its factorization.

1991871 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1193 (or 1181 counting only the distinct ones).

The product of its digits is 4536, while the sum is 36.

The square root of 1991871 is about 1411.3366005316. The cubic root of 1991871 is about 125.8211748945.

The spelling of 1991871 in words is "one million, nine hundred ninety-one thousand, eight hundred seventy-one".