81971905 has 16 divisors (see below), whose sum is σ = 101836800. Its totient is φ = 63276480.

The previous prime is 81971873. The next prime is 81971917. The reversal of 81971905 is 50917918.

It is a happy number.

It is not a de Polignac number, because 81971905 - 2⁵ = 81971873 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 78376 + ... + 79414.

It is an arithmetic number, because the mean of its divisors is an integer number (6364800).

Almost surely, 2^81971905 is an apocalyptic number.

It is an amenable number.

81971905 is a deficient number, since it is larger than the sum of its proper divisors (19864895).

81971905 is a wasteful number, since it uses less digits than its factorization.

81971905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1584.

The product of its (nonzero) digits is 22680, while the sum is 40.

The square root of 81971905 is about 9053.8337183759. The cubic root of 81971905 is about 434.3985257517.

The spelling of 81971905 in words is "eighty-one million, nine hundred seventy-one thousand, nine hundred five".