31643991 has 12 divisors (see below), whose sum is σ = 46943832. Its totient is φ = 20525616.

The previous prime is 31643957. The next prime is 31643993. The reversal of 31643991 is 19934613.

31643991 is a `hidden beast` number, since 3 + 1 + 643 + 9 + 9 + 1 = 666.

It is a de Polignac number, because none of the positive numbers 2^k-31643991 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31643993) 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, 47181 + ... + 47846.

It is an arithmetic number, because the mean of its divisors is an integer number (3911986).

Almost surely, 2^31643991 is an apocalyptic number.

31643991 is a deficient number, since it is larger than the sum of its proper divisors (15299841).

31643991 is a wasteful number, since it uses less digits than its factorization.

31643991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 95070 (or 95067 counting only the distinct ones).

The product of its digits is 17496, while the sum is 36.

The square root of 31643991 is about 5625.2991920430. The cubic root of 31643991 is about 316.2984648706.

The spelling of 31643991 in words is "thirty-one million, six hundred forty-three thousand, nine hundred ninety-one".