491999561 has 2 divisors, whose sum is σ = 491999562. Its totient is φ = 491999560.

The previous prime is 491999539. The next prime is 491999569. The reversal of 491999561 is 165999194.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 491287225 + 712336 = 22165^2 + 844^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-491999561 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (491999569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 245999780 + 245999781.

It is an arithmetic number, because the mean of its divisors is an integer number (245999781).

Almost surely, 2^491999561 is an apocalyptic number.

It is an amenable number.

491999561 is a deficient number, since it is larger than the sum of its proper divisors (1).

491999561 is an equidigital number, since it uses as much as digits as its factorization.

491999561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 787320, while the sum is 53.

The square root of 491999561 is about 22181.0631169924. The cubic root of 491999561 is about 789.4444424958. Note that the first 5 decimals are identical.

The spelling of 491999561 in words is "four hundred ninety-one million, nine hundred ninety-nine thousand, five hundred sixty-one".