991649505855 has 64 divisors (see below), whose sum is σ = 1624927703040. Its totient is φ = 516226054656.

The previous prime is 991649505851. The next prime is 991649505919. The reversal of 991649505855 is 558505946199.

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

It is not a de Polignac number, because 991649505855 - 2² = 991649505851 is a prime.

It is a Smith number, since the sum of its digits (66) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent 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 (23) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 158331454 + ... + 158337716.

It is an arithmetic number, because the mean of its divisors is an integer number (25389495360).

Almost surely, 2^991649505855 is an apocalyptic number.

991649505855 is a deficient number, since it is larger than the sum of its proper divisors (633278197185).

991649505855 is a wasteful number, since it uses less digits than its factorization.

991649505855 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7320.

The product of its (nonzero) digits is 87480000, while the sum is 66.

The spelling of 991649505855 in words is "nine hundred ninety-one billion, six hundred forty-nine million, five hundred five thousand, eight hundred fifty-five".