81991814 has 4 divisors (see below), whose sum is σ = 122987724. Its totient is φ = 40995906.

The previous prime is 81991813. The next prime is 81991817. The reversal of 81991814 is 41819918.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81991813) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20497952 + ... + 20497955.

It is an arithmetic number, because the mean of its divisors is an integer number (30746931).

Almost surely, 2^81991814 is an apocalyptic number.

81991814 is a deficient number, since it is larger than the sum of its proper divisors (40995910).

81991814 is a wasteful number, since it uses less digits than its factorization.

81991814 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40995909.

The product of its digits is 20736, while the sum is 41.

The square root of 81991814 is about 9054.9331306200. The cubic root of 81991814 is about 434.4336912155.

The spelling of 81991814 in words is "eighty-one million, nine hundred ninety-one thousand, eight hundred fourteen".