81991143 has 32 divisors (see below), whose sum is σ = 131604480. Its totient is φ = 50150880.

The previous prime is 81991141. The next prime is 81991157. The reversal of 81991143 is 34119918.

It is not a de Polignac number, because 81991143 - 2¹ = 81991141 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81991098 and 81991107.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81991141) 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, 66430 + ... + 67652.

It is an arithmetic number, because the mean of its divisors is an integer number (4112640).

Almost surely, 2^81991143 is an apocalyptic number.

81991143 is a deficient number, since it is larger than the sum of its proper divisors (49613337).

81991143 is a wasteful number, since it uses less digits than its factorization.

81991143 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1436 (or 1430 counting only the distinct ones).

The product of its digits is 7776, while the sum is 36.

The square root of 81991143 is about 9054.8960789177. The cubic root of 81991143 is about 434.4325061143.

The spelling of 81991143 in words is "eighty-one million, nine hundred ninety-one thousand, one hundred forty-three".