81400 has 48 divisors (see below), whose sum is σ = 212040. Its totient is φ = 28800.

The previous prime is 81373. The next prime is 81401. The reversal of 81400 is 418.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81401) by changing a digit.

It is a nontrivial repunit in base 43.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2182 + ... + 2218.

2⁸¹⁴⁰⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (106020).

81400 is an abundant number, since it is smaller than the sum of its proper divisors (130640).

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

81400 is a wasteful number, since it uses less digits than its factorization.

81400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64 (or 55 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 81400 is about 285.3068523537. The cubic root of 81400 is about 43.3385923926.

Adding to 81400 its reverse (418), we get a palindrome (81818).

It can be divided in two parts, 81 and 400, that multiplied together give a square (32400 = 180²).

The spelling of 81400 in words is "eighty-one thousand, four hundred".