81566669 has 4 divisors (see below), whose sum is σ = 81647580. Its totient is φ = 81485760.

The previous prime is 81566659. The next prime is 81566711. The reversal of 81566669 is 96666518.

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 27352900 + 54213769 = 5230^2 + 7363^2 .

It is a cyclic number.

It is not a de Polignac number, because 81566669 - 2⁸ = 81566413 is a prime.

It is a super-2 number, since 2×81566669² = 13306242983511122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81566659) 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, 38924 + ... + 40965.

It is an arithmetic number, because the mean of its divisors is an integer number (20411895).

Almost surely, 2^81566669 is an apocalyptic number.

It is an amenable number.

81566669 is a deficient number, since it is larger than the sum of its proper divisors (80911).

81566669 is a wasteful number, since it uses less digits than its factorization.

81566669 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80910.

The product of its digits is 466560, while the sum is 47.

The square root of 81566669 is about 9031.4267422152. The cubic root of 81566669 is about 433.6815126055.

The spelling of 81566669 in words is "eighty-one million, five hundred sixty-six thousand, six hundred sixty-nine".