81601997 has 4 divisors (see below), whose sum is σ = 81745980. Its totient is φ = 81458016.

The previous prime is 81601991. The next prime is 81602029. The reversal of 81601997 is 79910618.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 52722121 + 28879876 = 7261^2 + 5374^2 .

It is a cyclic number.

It is not a de Polignac number, because 81601997 - 2²⁶ = 14493133 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81601991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71138 + ... + 72275.

It is an arithmetic number, because the mean of its divisors is an integer number (20436495).

Almost surely, 2^81601997 is an apocalyptic number.

It is an amenable number.

81601997 is a deficient number, since it is larger than the sum of its proper divisors (143983).

81601997 is a wasteful number, since it uses less digits than its factorization.

81601997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 143982.

The product of its (nonzero) digits is 27216, while the sum is 41.

The square root of 81601997 is about 9033.3823676406. The cubic root of 81601997 is about 433.7441153379.

The spelling of 81601997 in words is "eighty-one million, six hundred one thousand, nine hundred ninety-seven".