31187991 has 4 divisors (see below), whose sum is σ = 41583992. Its totient is φ = 20791992.

The previous prime is 31187971. The next prime is 31188007. The reversal of 31187991 is 19978113.

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

It is not a de Polignac number, because 31187991 - 2⁶ = 31187927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31187941) 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, 5197996 + ... + 5198001.

It is an arithmetic number, because the mean of its divisors is an integer number (10395998).

Almost surely, 2^31187991 is an apocalyptic number.

31187991 is a deficient number, since it is larger than the sum of its proper divisors (10396001).

31187991 is a wasteful number, since it uses less digits than its factorization.

31187991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10396000.

The product of its digits is 13608, while the sum is 39.

The square root of 31187991 is about 5584.6209361066. The cubic root of 31187991 is about 314.7717873363.

The spelling of 31187991 in words is "thirty-one million, one hundred eighty-seven thousand, nine hundred ninety-one".