81911199 has 4 divisors (see below), whose sum is σ = 109214936. Its totient is φ = 54607464.

The previous prime is 81911197. The next prime is 81911201. The reversal of 81911199 is 99111918.

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

It is an interprime number because it is at equal distance from previous prime (81911197) and next prime (81911201).

It is not a de Polignac number, because 81911199 - 2¹ = 81911197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81911197) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13651864 + ... + 13651869.

It is an arithmetic number, because the mean of its divisors is an integer number (27303734).

Almost surely, 2^81911199 is an apocalyptic number.

81911199 is a deficient number, since it is larger than the sum of its proper divisors (27303737).

81911199 is a wasteful number, since it uses less digits than its factorization.

81911199 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27303736.

The product of its digits is 5832, while the sum is 39.

The square root of 81911199 is about 9050.4805949739. The cubic root of 81911199 is about 434.2912649800.

It can be divided in two parts, 8191119 and 9, that added together give a triangular number (8191128 = T₄₀₄₇).

The spelling of 81911199 in words is "eighty-one million, nine hundred eleven thousand, one hundred ninety-nine".