81971805 has 8 divisors (see below), whose sum is σ = 131154912. Its totient is φ = 43718288.

The previous prime is 81971767. The next prime is 81971821. The reversal of 81971805 is 50817918.

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

It is a cyclic number.

It is not a de Polignac number, because 81971805 - 2¹⁹ = 81447517 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, 2732379 + ... + 2732408.

It is an arithmetic number, because the mean of its divisors is an integer number (16394364).

Almost surely, 2^81971805 is an apocalyptic number.

It is an amenable number.

81971805 is a deficient number, since it is larger than the sum of its proper divisors (49183107).

81971805 is a wasteful number, since it uses less digits than its factorization.

81971805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5464795.

The product of its (nonzero) digits is 20160, while the sum is 39.

The square root of 81971805 is about 9053.8281958517. The cubic root of 81971805 is about 434.3983491063.

The spelling of 81971805 in words is "eighty-one million, nine hundred seventy-one thousand, eight hundred five".