It is a tau number, because it is divible by the number of its divisors (48).
It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.
It is a nialpdrome in base 12 and base 14.
It is a zygodrome in base 4 and base 14.
220640 is an apocalyptic number.
20640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 20640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33264).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
20640 is a wasteful number, since it uses less digits than its factorization.
20640 is an evil number, because the sum of its binary digits is even.
The square root of 20640 is about 143.6662799685. Note that the first 3 decimals coincide. The cubic root of 20640 is about 27.4306794015.
The spelling of 20640 in words is "twenty thousand, six hundred forty".