31991328 has 96 divisors (see below), whose sum is σ = 94993920. Its totient is φ = 10471680.

The previous prime is 31991327. The next prime is 31991329. The reversal of 31991328 is 82319913.

It is an interprime number because it is at equal distance from previous prime (31991327) and next prime (31991329).

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 31991292 and 31991301.

It is not an unprimeable number, because it can be changed into a prime (31991327) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 52401 + ... + 53007.

It is an arithmetic number, because the mean of its divisors is an integer number (989520).

Almost surely, 2^31991328 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 31991328, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (47496960).

31991328 is an abundant number, since it is smaller than the sum of its proper divisors (63002592).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

31991328 is a wasteful number, since it uses less digits than its factorization.

31991328 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 687 (or 673 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 31991328 is about 5656.0876938039. The cubic root of 31991328 is about 317.4515287569.

The spelling of 31991328 in words is "thirty-one million, nine hundred ninety-one thousand, three hundred twenty-eight".