81000081000021 has 8 divisors (see below), whose sum is σ = 108009323859520. Its totient is φ = 53995446070272.

The previous prime is 81000081000011. The next prime is 81000081000109. The reversal of 81000081000021 is 12000018000018.

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

It is not a de Polignac number, because 81000081000021 - 2⁵ = 81000080999989 is a prime.

It is a super-2 number, since 2×81000081000021² (a number of 29 digits) contains 22 as substring.

It is the 9000005-th Hogben number.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81000081000011) by changing a digit.

It is a nontrivial repunit in base 9000004.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1151941420 + ... + 1152011733.

It is an arithmetic number, because the mean of its divisors is an integer number (13501165482440).

Almost surely, 2^{81000081000021} is an apocalyptic number.

It is an amenable number.

81000081000021 is a deficient number, since it is larger than the sum of its proper divisors (27009242859499).

81000081000021 is a wasteful number, since it uses less digits than its factorization.

81000081000021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2303964875.

The product of its (nonzero) digits is 128, while the sum is 21.

Adding to 81000081000021 its reverse (12000018000018), we get a palindrome (93000099000039).

The spelling of 81000081000021 in words is "eighty-one trillion, eighty-one million, twenty-one", and thus it is an aban number and an uban number.