• 990 can be written using four 4's:

See also 113.

---

990 has 24 divisors (see below), whose sum is σ = 2808. Its totient is φ = 240.

The previous prime is 983. The next prime is 991. The reversal of 990 is 99.

Added to its reverse (99) it gives a square (1089 = 33²).

990 = 12² + 13² + ... + 16².

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 nontrivial binomial coefficient, being equal to C(45, 2).

990 is a Gilda number.

It is a Harshad number since it is a multiple of its sum of digits (18).

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.

It is not an unprimeable number, because it can be changed into a prime (991) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 85 + ... + 95.

It is an arithmetic number, because the mean of its divisors is an integer number (117).

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).

990 is an abundant number, since it is smaller than the sum of its proper divisors (1818).

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 sum of its prime factors is 24 (or 21 counting only the distinct ones).

The product of its (nonzero) digits is 81, while the sum is 18.

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).

It can be divided in two parts, 9 and 90, that added together give a palindrome (99).

The spelling of 990 in words is "nine hundred ninety", and thus it is an aban number and an oban number.