• 990 can be written using four 4's:
990 is nontrivially palindromic in base 12.
990 is digitally balanced in base 5, because in such base it contains all the possibile digits an equal number of times.
990 is a Gilda number.
It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.
990 is an undulating number in base 12.
990 is strictly pandigital in base 5.
It is a plaindrome in base 16.
It is a nialpdrome in base 6, base 10 and base 11.
It is a congruent number.
990 is a gapful number since it is divisible by the number (90) formed by its first and last digit.
990 is the 44-th triangular number.
It is a practical number, because each smaller number is the sum of distinct divisors of 990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1404).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
990 is a wasteful number, since it uses less digits than its factorization.
990 is an evil number, because the sum of its binary digits is even.
The square root of 990 is about 31.4642654451. The cubic root of 990 is about 9.9665549341.
990 divided by its sum of digits (18) gives a palindrome (55).
Subtracting from 990 its product of nonzero digits (81), we obtain a palindrome (909).
Adding to 990 its reverse (99), we get a square (1089 = 332).