81605693 has 4 divisors (see below), whose sum is σ = 87883068. Its totient is φ = 75328320.

The previous prime is 81605659. The next prime is 81605707. The reversal of 81605693 is 39650618.

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 38217124 + 43388569 = 6182^2 + 6587^2 .

It is a cyclic number.

It is not a de Polignac number, because 81605693 - 2²⁰ = 80557117 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81605603) 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, 3138668 + ... + 3138693.

It is an arithmetic number, because the mean of its divisors is an integer number (21970767).

Almost surely, 2^81605693 is an apocalyptic number.

It is an amenable number.

81605693 is a deficient number, since it is larger than the sum of its proper divisors (6277375).

81605693 is a wasteful number, since it uses less digits than its factorization.

81605693 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6277374.

The product of its (nonzero) digits is 38880, while the sum is 38.

The square root of 81605693 is about 9033.5869398595. The cubic root of 81605693 is about 433.7506637644.

The spelling of 81605693 in words is "eighty-one million, six hundred five thousand, six hundred ninety-three".