991649505791 has 8 divisors (see below), whose sum is σ = 1133319795744. Its totient is φ = 849980734560.

The previous prime is 991649505787. The next prime is 991649505793. The reversal of 991649505791 is 197505946199.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 991649505791 - 2² = 991649505787 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991649505793) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2093621 + ... + 2523201.

It is an arithmetic number, because the mean of its divisors is an integer number (141664974468).

Almost surely, 2^991649505791 is an apocalyptic number.

991649505791 is a deficient number, since it is larger than the sum of its proper divisors (141670289953).

991649505791 is a wasteful number, since it uses less digits than its factorization.

991649505791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 759361.

The product of its (nonzero) digits is 27556200, while the sum is 65.

Adding to 991649505791 its sum of digits (65), we get a square (991649505856 = 995816²).

The spelling of 991649505791 in words is "nine hundred ninety-one billion, six hundred forty-nine million, five hundred five thousand, seven hundred ninety-one".