81505191 has 32 divisors (see below), whose sum is σ = 120821760. Its totient is φ = 48646656.

The previous prime is 81505183. The next prime is 81505199. The reversal of 81505191 is 19150518.

It is an interprime number because it is at equal distance from previous prime (81505183) and next prime (81505199).

It is not a de Polignac number, because 81505191 - 2³ = 81505183 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81505199) 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 31 ways as a sum of consecutive naturals, for example, 88230 + ... + 89148.

It is an arithmetic number, because the mean of its divisors is an integer number (3775680).

Almost surely, 2^81505191 is an apocalyptic number.

81505191 is a deficient number, since it is larger than the sum of its proper divisors (39316569).

81505191 is a wasteful number, since it uses less digits than its factorization.

81505191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1023.

The product of its (nonzero) digits is 1800, while the sum is 30.

The square root of 81505191 is about 9028.0225409555. The cubic root of 81505191 is about 433.5725278382.

The spelling of 81505191 in words is "eighty-one million, five hundred five thousand, one hundred ninety-one".