81566921 has 8 divisors (see below), whose sum is σ = 84768000.
Its totient is φ = 78401520.
The previous prime is 81566909. The next prime is 81566941. The reversal of 81566921 is 12966518.
It is a sphenic number, since it is the product of 3 distinct primes.
It is a cyclic number.
It is not a de Polignac number, because 81566921 - 26 = 81566857 is a prime.
It is a Duffinian number.
It is not an unprimeable number, because it can be changed into a prime (81566941) 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, 4211 + ... + 13448.
It is an arithmetic number, because the mean of its divisors is an integer number (10596000).
Almost surely, 281566921 is an apocalyptic number.
It is an amenable number.
81566921 is a deficient number, since it is larger than the sum of its proper divisors (3201079).
81566921 is a wasteful number, since it uses less digits than its factorization.
81566921 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 17839.
The product of its digits is 25920, while the sum is 38.
The square root of 81566921 is about 9031.4406934885.
The cubic root of 81566921 is about 433.6819592243.
The spelling of 81566921 in words is "eighty-one million, five hundred sixty-six thousand, nine hundred twenty-one".