81640 has 32 divisors (see below), whose sum is σ = 199080. Its totient is φ = 29952.

The previous prime is 81637. The next prime is 81647. The reversal of 81640 is 4618.

It can be written as a sum of positive squares in 4 ways, for example, as 42436 + 39204 = 206^2 + 198^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81647) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 442 + ... + 598.

2⁸¹⁶⁴⁰ 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 81640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99540).

81640 is an abundant number, since it is smaller than the sum of its proper divisors (117440).

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

81640 is a wasteful number, since it uses less digits than its factorization.

81640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 181 (or 177 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 81640 is about 285.7271425679. The cubic root of 81640 is about 43.3811438116.

It can be divided in two parts, 816 and 40, that multiplied together give a triangular number (32640 = T₂₅₅).

The spelling of 81640 in words is "eighty-one thousand, six hundred forty".