81659821 has 8 divisors (see below), whose sum is σ = 87024384. Its totient is φ = 76446480.

The previous prime is 81659819. The next prime is 81659833. The reversal of 81659821 is 12895618.

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

It is not a de Polignac number, because 81659821 - 2¹ = 81659819 is a prime.

It is a super-3 number, since 3×81659821³ (a number of 25 digits) contains 333 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 (81659521) 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, 36690 + ... + 38851.

It is an arithmetic number, because the mean of its divisors is an integer number (10878048).

Almost surely, 2^81659821 is an apocalyptic number.

It is an amenable number.

81659821 is a deficient number, since it is larger than the sum of its proper divisors (5364563).

81659821 is a wasteful number, since it uses less digits than its factorization.

81659821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75611.

The product of its digits is 34560, while the sum is 40.

The square root of 81659821 is about 9036.5823738845. The cubic root of 81659821 is about 433.8465429696.

The spelling of 81659821 in words is "eighty-one million, six hundred fifty-nine thousand, eight hundred twenty-one".