81808 has 10 divisors (see below), whose sum is σ = 158534. Its totient is φ = 40896.

The previous prime is 81799. The next prime is 81817. The reversal of 81808 is 80818.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (81799) and next prime (81817).

It can be written as a sum of positive squares in only one way, i.e., 44944 + 36864 = 212^2 + 192^2 .

It is an Ulam number.

It is an unprimeable number.

81808 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2541 + ... + 2572.

2⁸¹⁸⁰⁸ is an apocalyptic number.

It is an amenable number.

81808 is a deficient number, since it is larger than the sum of its proper divisors (76726).

81808 is a wasteful number, since it uses less digits than its factorization.

81808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5121 (or 5115 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 25.

The square root of 81808 is about 286.0209782516. The cubic root of 81808 is about 43.4108802101.

Subtracting from 81808 its reverse (80818), we obtain a triangular number (990 = T₄₄).

The spelling of 81808 in words is "eighty-one thousand, eight hundred eight".