71991 has 12 divisors (see below), whose sum is σ = 109720. Its totient is φ = 45360.

The previous prime is 71987. The next prime is 71993. The reversal of 71991 is 19917.

It is not a de Polignac number, because 71991 - 2² = 71987 is a prime.

It is a Duffinian number.

71991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (71993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 40 + ... + 381.

2⁷¹⁹⁹¹ is an apocalyptic number.

71991 is a deficient number, since it is larger than the sum of its proper divisors (37729).

71991 is a wasteful number, since it uses less digits than its factorization.

71991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 446 (or 443 counting only the distinct ones).

The product of its digits is 567, while the sum is 27.

The square root of 71991 is about 268.3113862660. The cubic root of 71991 is about 41.5999429856.

The spelling of 71991 in words is "seventy-one thousand, nine hundred ninety-one".