31638991 has 2 divisors, whose sum is σ = 31638992. Its totient is φ = 31638990.

The previous prime is 31638977. The next prime is 31639021. The reversal of 31638991 is 19983613.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 31638991 - 2⁷ = 31638863 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31638491) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15819495 + 15819496.

It is an arithmetic number, because the mean of its divisors is an integer number (15819496).

Almost surely, 2^31638991 is an apocalyptic number.

31638991 is a deficient number, since it is larger than the sum of its proper divisors (1).

31638991 is an equidigital number, since it uses as much as digits as its factorization.

31638991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34992, while the sum is 40.

The square root of 31638991 is about 5624.8547536803. The cubic root of 31638991 is about 316.2818047763.

The spelling of 31638991 in words is "thirty-one million, six hundred thirty-eight thousand, nine hundred ninety-one".