81990 has 24 divisors (see below), whose sum is σ = 213408. Its totient is φ = 21840.

The previous prime is 81973. The next prime is 82003. The reversal of 81990 is 9918.

It is a Curzon number.

It is a plaindrome in base 11.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 81990.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 366 + ... + 545.

It is an arithmetic number, because the mean of its divisors is an integer number (8892).

2⁸¹⁹⁹⁰ is an apocalyptic number.

81990 is an abundant number, since it is smaller than the sum of its proper divisors (131418).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (106704).

81990 is a wasteful number, since it uses less digits than its factorization.

81990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 924 (or 921 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 27.

The square root of 81990 is about 286.3389599758. The cubic root of 81990 is about 43.4430487365.

It can be divided in two parts, 819 and 90, that added together give a palindrome (909).

The spelling of 81990 in words is "eighty-one thousand, nine hundred ninety".