991649505857 has 4 divisors (see below), whose sum is σ = 998887823556. Its totient is φ = 984411188160.

The previous prime is 991649505851. The next prime is 991649505919. The reversal of 991649505857 is 758505946199.

It is a Cunningham number, because it is equal to 995816²+1.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 582498662656 + 409150843201 = 763216^2 + 639649^2 .

It is a cyclic number.

It is not a de Polignac number, because 991649505857 - 2⁶ = 991649505793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991649505851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3619158644 + ... + 3619158917.

It is an arithmetic number, because the mean of its divisors is an integer number (249721955889).

Almost surely, 2^991649505857 is an apocalyptic number.

It is an amenable number.

991649505857 is a deficient number, since it is larger than the sum of its proper divisors (7238317699).

991649505857 is a wasteful number, since it uses less digits than its factorization.

991649505857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7238317698.

The product of its (nonzero) digits is 122472000, while the sum is 68.

The spelling of 991649505857 in words is "nine hundred ninety-one billion, six hundred forty-nine million, five hundred five thousand, eight hundred fifty-seven".