491191681 has 2 divisors, whose sum is σ = 491191682. Its totient is φ = 491191680.

The previous prime is 491191639. The next prime is 491191721. The reversal of 491191681 is 186191194.

It is an a-pointer prime, because the next prime (491191721) can be obtained adding 491191681 to its sum of digits (40).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 483120400 + 8071281 = 21980^2 + 2841^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-491191681 is a prime.

It is a super-2 number, since 2×491191681² = 482538534967211522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (491191601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 245595840 + 245595841.

It is an arithmetic number, because the mean of its divisors is an integer number (245595841).

Almost surely, 2^491191681 is an apocalyptic number.

It is an amenable number.

491191681 is a deficient number, since it is larger than the sum of its proper divisors (1).

491191681 is an equidigital number, since it uses as much as digits as its factorization.

491191681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 40.

The square root of 491191681 is about 22162.8446053299. The cubic root of 491191681 is about 789.0121075717.

The spelling of 491191681 in words is "four hundred ninety-one million, one hundred ninety-one thousand, six hundred eighty-one".