12171991 has 8 divisors (see below), whose sum is σ = 13678560. Its totient is φ = 10746912.

The previous prime is 12171979. The next prime is 12171997. The reversal of 12171991 is 19917121.

It is a happy number.

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 12171991 - 2²¹ = 10074839 is a prime.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12171997) 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, 20056 + ... + 20653.

It is an arithmetic number, because the mean of its divisors is an integer number (1709820).

Almost surely, 2^12171991 is an apocalyptic number.

12171991 is a deficient number, since it is larger than the sum of its proper divisors (1506569).

12171991 is a wasteful number, since it uses less digits than its factorization.

12171991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40745.

The product of its digits is 1134, while the sum is 31.

The square root of 12171991 is about 3488.8380587238. The cubic root of 12171991 is about 230.0314449761.

The spelling of 12171991 in words is "twelve million, one hundred seventy-one thousand, nine hundred ninety-one".