81666681 has 8 divisors (see below), whose sum is σ = 109967424. Its totient is φ = 53905200.

The previous prime is 81666671. The next prime is 81666701. The reversal of 81666681 is 18666618.

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

It is not a de Polignac number, because 81666681 - 2⁵ = 81666649 is a prime.

It is a super-2 number, since 2×81666681² = 13338893571111522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81666601) 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, 134461 + ... + 135066.

It is an arithmetic number, because the mean of its divisors is an integer number (13745928).

Almost surely, 2^81666681 is an apocalyptic number.

It is an amenable number.

81666681 is a deficient number, since it is larger than the sum of its proper divisors (28300743).

81666681 is a wasteful number, since it uses less digits than its factorization.

81666681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 269631.

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

The square root of 81666681 is about 9036.9619341901. The cubic root of 81666681 is about 433.8586913510.

The spelling of 81666681 in words is "eighty-one million, six hundred sixty-six thousand, six hundred eighty-one".