1981881891 has 32 divisors (see below), whose sum is σ = 3246954240. Its totient is φ = 1184673600.

The previous prime is 1981881817. The next prime is 1981881899.

1981881891 is nontrivially palindromic in base 10.

It is not a de Polignac number, because 1981881891 - 2⁹ = 1981881379 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1981881899) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 24025 + ... + 67386.

It is an arithmetic number, because the mean of its divisors is an integer number (101467320).

Almost surely, 2^1981881891 is an apocalyptic number.

1981881891 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1981881891 is a deficient number, since it is larger than the sum of its proper divisors (1265072349).

1981881891 is a wasteful number, since it uses less digits than its factorization.

1981881891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91504 (or 91498 counting only the distinct ones).

The product of its digits is 331776, while the sum is 54.

The square root of 1981881891 is about 44518.3320779204. The cubic root of 1981881891 is about 1256.1049386523.

The spelling of 1981881891 in words is "one billion, nine hundred eighty-one million, eight hundred eighty-one thousand, eight hundred ninety-one".