2171991 has 4 divisors (see below), whose sum is σ = 2895992. Its totient is φ = 1447992.

The previous prime is 2171989. The next prime is 2171999. The reversal of 2171991 is 1991712.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 2171991 - 2¹ = 2171989 is a prime.

It is a D-number.

It is a Duffinian number.

2171991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2171999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 361996 + ... + 362001.

It is an arithmetic number, because the mean of its divisors is an integer number (723998).

2^2171991 is an apocalyptic number.

2171991 is a deficient number, since it is larger than the sum of its proper divisors (724001).

2171991 is an equidigital number, since it uses as much as digits as its factorization.

2171991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 724000.

The product of its digits is 1134, while the sum is 30.

The square root of 2171991 is about 1473.7676207598. The cubic root of 2171991 is about 129.5048422234.

The spelling of 2171991 in words is "two million, one hundred seventy-one thousand, nine hundred ninety-one".