81191985 has 32 divisors (see below), whose sum is σ = 149560320. Its totient is φ = 36842688.

The previous prime is 81191977. The next prime is 81191993. The reversal of 81191985 is 58919118.

It is an interprime number because it is at equal distance from previous prime (81191977) and next prime (81191993).

It is not a de Polignac number, because 81191985 - 2³ = 81191977 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 11814 + ... + 17376.

It is an arithmetic number, because the mean of its divisors is an integer number (4673760).

Almost surely, 2^81191985 is an apocalyptic number.

It is an amenable number.

81191985 is a deficient number, since it is larger than the sum of its proper divisors (68368335).

81191985 is a wasteful number, since it uses less digits than its factorization.

81191985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5717.

The product of its digits is 25920, while the sum is 42.

The square root of 81191985 is about 9010.6595208120. The cubic root of 81191985 is about 433.0164412292.

The spelling of 81191985 in words is "eighty-one million, one hundred ninety-one thousand, nine hundred eighty-five".