81668661 has 8 divisors (see below), whose sum is σ = 109043040. Its totient is φ = 54370032.

The previous prime is 81668659. The next prime is 81668683. The reversal of 81668661 is 16686618.

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

It is not a de Polignac number, because 81668661 - 2¹ = 81668659 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81668641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16371 + ... + 20768.

It is an arithmetic number, because the mean of its divisors is an integer number (13630380).

Almost surely, 2^81668661 is an apocalyptic number.

It is an amenable number.

81668661 is a deficient number, since it is larger than the sum of its proper divisors (27374379).

81668661 is a wasteful number, since it uses less digits than its factorization.

81668661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37875.

The product of its digits is 82944, while the sum is 42.

The square root of 81668661 is about 9037.0714836168. The cubic root of 81668661 is about 433.8621976086.

The spelling of 81668661 in words is "eighty-one million, six hundred sixty-eight thousand, six hundred sixty-one".