31991513 has 2 divisors, whose sum is σ = 31991514. Its totient is φ = 31991512.

The previous prime is 31991507. The next prime is 31991539. The reversal of 31991513 is 31519913.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16999129 + 14992384 = 4123^2 + 3872^2 .

It is a cyclic number.

It is not a de Polignac number, because 31991513 - 2¹⁰ = 31990489 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 31991513.

It is not a weakly prime, because it can be changed into another prime (31991503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15995756 + 15995757.

It is an arithmetic number, because the mean of its divisors is an integer number (15995757).

Almost surely, 2^31991513 is an apocalyptic number.

It is an amenable number.

31991513 is a deficient number, since it is larger than the sum of its proper divisors (1).

31991513 is an equidigital number, since it uses as much as digits as its factorization.

31991513 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3645, while the sum is 32.

The square root of 31991513 is about 5656.1040478407. The cubic root of 31991513 is about 317.4521406771.

The spelling of 31991513 in words is "thirty-one million, nine hundred ninety-one thousand, five hundred thirteen".