81660 has 24 divisors (see below), whose sum is σ = 228816. Its totient is φ = 21760.

The previous prime is 81649. The next prime is 81667. The reversal of 81660 is 6618.

It is a hoax number, since the sum of its digits (21) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81667) by changing a digit.

81660 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 621 + ... + 740.

It is an arithmetic number, because the mean of its divisors is an integer number (9534).

2⁸¹⁶⁶⁰ is an apocalyptic number.

It is an amenable number.

81660 is an abundant number, since it is smaller than the sum of its proper divisors (147156).

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 (114408).

81660 is a wasteful number, since it uses less digits than its factorization.

81660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1373 (or 1371 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 81660 is about 285.7621388498. The cubic root of 81660 is about 43.3846859970.

It can be divided in two parts, 81 and 660, that added together give a triangular number (741 = T₃₈).

The spelling of 81660 in words is "eighty-one thousand, six hundred sixty".