31312991 has 4 divisors (see below), whose sum is σ = 31453632. Its totient is φ = 31172352.

The previous prime is 31312973. The next prime is 31312999. The reversal of 31312991 is 19921313.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19921313 = 31 ⋅642623.

It is a cyclic number.

It is not a de Polignac number, because 31312991 - 2¹⁸ = 31050847 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 (31312999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 69986 + ... + 70431.

It is an arithmetic number, because the mean of its divisors is an integer number (7863408).

Almost surely, 2^31312991 is an apocalyptic number.

31312991 is a deficient number, since it is larger than the sum of its proper divisors (140641).

31312991 is a wasteful number, since it uses less digits than its factorization.

31312991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 140640.

The product of its digits is 1458, while the sum is 29.

The square root of 31312991 is about 5595.8011937523. The cubic root of 31312991 is about 315.1917569316.

The spelling of 31312991 in words is "thirty-one million, three hundred twelve thousand, nine hundred ninety-one".