1991331457 has 2 divisors, whose sum is σ = 1991331458. Its totient is φ = 1991331456.

The previous prime is 1991331443. The next prime is 1991331473. The reversal of 1991331457 is 7541331991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1868919361 + 122412096 = 43231^2 + 11064^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991331457 is a prime.

It is not a weakly prime, because it can be changed into another prime (1991331497) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995665728 + 995665729.

It is an arithmetic number, because the mean of its divisors is an integer number (995665729).

Almost surely, 2^1991331457 is an apocalyptic number.

It is an amenable number.

1991331457 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991331457 is an equidigital number, since it uses as much as digits as its factorization.

1991331457 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 102060, while the sum is 43.

The square root of 1991331457 is about 44624.3370482969. The cubic root of 1991331457 is about 1258.0981337152.

The spelling of 1991331457 in words is "one billion, nine hundred ninety-one million, three hundred thirty-one thousand, four hundred fifty-seven".