31691813 has 2 divisors, whose sum is σ = 31691814. Its totient is φ = 31691812.

The previous prime is 31691801. The next prime is 31691819. The reversal of 31691813 is 31819613.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 22829284 + 8862529 = 4778^2 + 2977^2 .

It is a cyclic number.

It is not a de Polignac number, because 31691813 - 2⁴ = 31691797 is a prime.

It is a super-2 number, since 2×31691813² = 2008742022453938, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 31691813.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31691819) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15845906 + 15845907.

It is an arithmetic number, because the mean of its divisors is an integer number (15845907).

Almost surely, 2^31691813 is an apocalyptic number.

It is an amenable number.

31691813 is a deficient number, since it is larger than the sum of its proper divisors (1).

31691813 is an equidigital number, since it uses as much as digits as its factorization.

31691813 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3888, while the sum is 32.

The square root of 31691813 is about 5629.5482056733. The cubic root of 31691813 is about 316.4577200863.

It can be divided in two parts, 316 and 91813, that added together give a palindrome (92129).

The spelling of 31691813 in words is "thirty-one million, six hundred ninety-one thousand, eight hundred thirteen".