81990720165 has 8 divisors (see below), whose sum is σ = 131185152288. Its totient is φ = 43728384080.

The previous prime is 81990720151. The next prime is 81990720167. The reversal of 81990720165 is 56102709918.

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

It is not a de Polignac number, because 81990720165 - 2¹⁰ = 81990719141 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81990720167) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2733023991 + ... + 2733024020.

It is an arithmetic number, because the mean of its divisors is an integer number (16398144036).

Almost surely, 2^81990720165 is an apocalyptic number.

It is an amenable number.

81990720165 is a deficient number, since it is larger than the sum of its proper divisors (49194432123).

81990720165 is a wasteful number, since it uses less digits than its factorization.

81990720165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5466048019.

The product of its (nonzero) digits is 272160, while the sum is 48.

The spelling of 81990720165 in words is "eighty-one billion, nine hundred ninety million, seven hundred twenty thousand, one hundred sixty-five".