81691286 has 4 divisors (see below), whose sum is σ = 122536932. Its totient is φ = 40845642.

The previous prime is 81691283. The next prime is 81691297. The reversal of 81691286 is 68219618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 68219618 = 2 ⋅34109809.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81691283) by changing a digit.

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 as a sum of consecutive naturals, namely, 20422820 + ... + 20422823.

It is an arithmetic number, because the mean of its divisors is an integer number (30634233).

Almost surely, 2^81691286 is an apocalyptic number.

81691286 is a deficient number, since it is larger than the sum of its proper divisors (40845646).

81691286 is a wasteful number, since it uses less digits than its factorization.

81691286 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40845645.

The product of its digits is 41472, while the sum is 41.

The square root of 81691286 is about 9038.3231851931. The cubic root of 81691286 is about 433.9022587768.

The spelling of 81691286 in words is "eighty-one million, six hundred ninety-one thousand, two hundred eighty-six".