81721081 has 8 divisors (see below), whose sum is σ = 88079040. Its totient is φ = 75373392.

The previous prime is 81721051. The next prime is 81721103. The reversal of 81721081 is 18012718.

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 81721081 - 2⁷ = 81720953 is a prime.

It is a super-2 number, since 2×81721081² = 13356670159617122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81721021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24966 + ... + 28048.

It is an arithmetic number, because the mean of its divisors is an integer number (11009880).

Almost surely, 2^81721081 is an apocalyptic number.

It is an amenable number.

81721081 is a deficient number, since it is larger than the sum of its proper divisors (6357959).

81721081 is a wasteful number, since it uses less digits than its factorization.

81721081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5135.

The product of its (nonzero) digits is 896, while the sum is 28.

The square root of 81721081 is about 9039.9712942022. The cubic root of 81721081 is about 433.9550042898.

Adding to 81721081 its reverse (18012718), we get a palindrome (99733799).

The spelling of 81721081 in words is "eighty-one million, seven hundred twenty-one thousand, eighty-one".