1991705856 has 576 divisors, whose sum is σ = 7158251520. Its totient is φ = 477757440.

The previous prime is 1991705827. The next prime is 1991705857. The reversal of 1991705856 is 6585071991.

It is a Harshad number since it is a multiple of its sum of digits (51).

It is a junction number, because it is equal to n+sod(n) for n = 1991705799 and 1991705808.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991705857) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 53829870 + ... + 53829906.

It is an arithmetic number, because the mean of its divisors is an integer number (12427520).

Almost surely, 2^1991705856 is an apocalyptic number.

1991705856 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1991705856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3579125760).

1991705856 is an abundant number, since it is smaller than the sum of its proper divisors (5166545664).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1991705856 is a wasteful number, since it uses less digits than its factorization.

1991705856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130 (or 116 counting only the distinct ones).

The product of its (nonzero) digits is 680400, while the sum is 51.

The square root of 1991705856 is about 44628.5318602349. The cubic root of 1991705856 is about 1258.1769756318.

The spelling of 1991705856 in words is "one billion, nine hundred ninety-one million, seven hundred five thousand, eight hundred fifty-six".