31172991 has 4 divisors (see below), whose sum is σ = 41563992. Its totient is φ = 20781992.

The previous prime is 31172989. The next prime is 31173001. The reversal of 31172991 is 19927113.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19927113 = 3 ⋅6642371.

It is a cyclic number.

It is not a de Polignac number, because 31172991 - 2¹ = 31172989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31172191) 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, 5195496 + ... + 5195501.

It is an arithmetic number, because the mean of its divisors is an integer number (10390998).

Almost surely, 2^31172991 is an apocalyptic number.

31172991 is a deficient number, since it is larger than the sum of its proper divisors (10391001).

31172991 is a wasteful number, since it uses less digits than its factorization.

31172991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10391000.

The product of its digits is 3402, while the sum is 33.

The square root of 31172991 is about 5583.2778007189. The cubic root of 31172991 is about 314.7213156235.

The spelling of 31172991 in words is "thirty-one million, one hundred seventy-two thousand, nine hundred ninety-one".