81997815 has 8 divisors (see below), whose sum is σ = 131196528. Its totient is φ = 43732160.

The previous prime is 81997789. The next prime is 81997823. The reversal of 81997815 is 51879918.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81997815 - 2¹⁰ = 81996791 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2733246 + ... + 2733275.

It is an arithmetic number, because the mean of its divisors is an integer number (16399566).

Almost surely, 2^81997815 is an apocalyptic number.

81997815 is a deficient number, since it is larger than the sum of its proper divisors (49198713).

81997815 is a wasteful number, since it uses less digits than its factorization.

81997815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5466529.

The product of its digits is 181440, while the sum is 48.

The square root of 81997815 is about 9055.2644908915. The cubic root of 81997815 is about 434.4442897247. Note that the first 3 decimals are identical.

The spelling of 81997815 in words is "eighty-one million, nine hundred ninety-seven thousand, eight hundred fifteen".