1981921856 has 56 divisors (see below), whose sum is σ = 4018102200. Its totient is φ = 969592832.

The previous prime is 1981921819. The next prime is 1981921859. The reversal of 1981921856 is 6581291891.

It can be written as a sum of positive squares in 4 ways, for example, as 459673600 + 1522248256 = 21440^2 + 39016^2 .

It is not an unprimeable number, because it can be changed into a prime (1981921859) 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 7 ways as a sum of consecutive naturals, for example, 1888820 + ... + 1889868.

It is an arithmetic number, because the mean of its divisors is an integer number (71751825).

Almost surely, 2^1981921856 is an apocalyptic number.

1981921856 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 1981921856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2009051100).

1981921856 is an abundant number, since it is smaller than the sum of its proper divisors (2036180344).

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

1981921856 is a wasteful number, since it uses less digits than its factorization.

1981921856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1671 (or 1661 counting only the distinct ones).

The product of its digits is 311040, while the sum is 50.

The square root of 1981921856 is about 44518.7809356905. The cubic root of 1981921856 is about 1256.1133817885.

The spelling of 1981921856 in words is "one billion, nine hundred eighty-one million, nine hundred twenty-one thousand, eight hundred fifty-six".