81908518 has 4 divisors (see below), whose sum is σ = 122862780. Its totient is φ = 40954258.

The previous prime is 81908513. The next prime is 81908537. The reversal of 81908518 is 81580918.

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

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81908513) 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, 20477128 + ... + 20477131.

It is an arithmetic number, because the mean of its divisors is an integer number (30715695).

Almost surely, 2^81908518 is an apocalyptic number.

81908518 is a deficient number, since it is larger than the sum of its proper divisors (40954262).

81908518 is a wasteful number, since it uses less digits than its factorization.

81908518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40954261.

The product of its (nonzero) digits is 23040, while the sum is 40.

The square root of 81908518 is about 9050.3324800805. The cubic root of 81908518 is about 434.2865267285.

The spelling of 81908518 in words is "eighty-one million, nine hundred eight thousand, five hundred eighteen".