1981001891 has 32 divisors (see below), whose sum is σ = 2396998656. Its totient is φ = 1614976000.

The previous prime is 1981001887. The next prime is 1981001909.

1981001891 is nontrivially palindromic in base 10.

It is not a de Polignac number, because 1981001891 - 2² = 1981001887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1981001801) 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, 1336871 + ... + 1338351.

It is an arithmetic number, because the mean of its divisors is an integer number (74906208).

Almost surely, 2^1981001891 is an apocalyptic number.

1981001891 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

1981001891 is a deficient number, since it is larger than the sum of its proper divisors (415996765).

1981001891 is a wasteful number, since it uses less digits than its factorization.

1981001891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1843.

The product of its (nonzero) digits is 5184, while the sum is 38.

The square root of 1981001891 is about 44508.4474116993. The cubic root of 1981001891 is about 1255.9189982094.

It can be divided in two parts, 198100 and 1891, that added together give a palindrome (199991).

The spelling of 1981001891 in words is "one billion, nine hundred eighty-one million, one thousand, eight hundred ninety-one".