2161991 has 8 divisors (see below), whose sum is σ = 2451120. Its totient is φ = 1890432.

The previous prime is 2161987. The next prime is 2162003. The reversal of 2161991 is 1991612.

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 2161991 - 2² = 2161987 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2161591) 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, 4130 + ... + 4623.

It is an arithmetic number, because the mean of its divisors is an integer number (306390).

2^2161991 is an apocalyptic number.

2161991 is a deficient number, since it is larger than the sum of its proper divisors (289129).

2161991 is a wasteful number, since it uses less digits than its factorization.

2161991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8785.

The product of its digits is 972, while the sum is 29.

The square root of 2161991 is about 1470.3710416082. The cubic root of 2161991 is about 129.3057866073.

The spelling of 2161991 in words is "two million, one hundred sixty-one thousand, nine hundred ninety-one".