999

999 < 998 | 1000 >
All Numbers
900	901	902	903	904	905	906	907	908	909
910	911	912	913	914	915	916	917	918	919
920	921	922	923	924	925	926	927	928	929
930	931	932	933	934	935	936	937	938	939
940	941	942	943	944	945	946	947	948	949
950	951	952	953	954	955	956	957	958	959
960	961	962	963	964	965	966	967	968	969
970	971	972	973	974	975	976	977	978	979
980	981	982	983	984	985	986	987	988	989
990	991	992	993	994	995	996	997	998	999

999 is the largest three-digit number in decimal, which led to its use in pete-5.c and pete-8.c.

Properties

• Its factors are 1, 3, 9, 27, 37, 111, 333 and 999, making it a composite number.
• 999 is an odd number.
• 999 is an unhappy number.
  

• 999 is deficient.
  
• Its prime factorization is 3³ × 37¹.
  
• 999 is a repdigit number, meaning it consists of one digit.
  
• It is (not considering myriad, lakh and -illiard) the largest number with an accepted English name not containing the letter “o” (namely, nine hundred ninety-nine).

• 999 is the 8th Kaprekar number.

• 999 is the United Kingdom's emergency telephone number. It was launched in 1937 is the world's first emergency telephone number.

Approximations

Notation	Lower bound	Upper bound
Up-arrow notation	10 ↑ 3
Scientific notation	\(9.99\times10^2\)	\(9.991\times10^2\)
Slow-growing hierarchy	\(g_{\omega^{\omega}}(4)\)	\(g_{\omega^{\omega}}(5)\)
Copy notation	9[3]	9[3]
Chained arrow notation	10 → 3
Bowers' Exploding Array Function/Bird's array notation	{10,3}
Fast-growing hierarchy	f2(7)	f2(8)
Hardy hierarchy	Hω(499)	Hω(500)
Middle-growing hierarchy	m(ω,9)	m(ω,10)
Hyper-E notation	E2.9996
Hyper-E notation (non-10 base)	\(E[10]3\)
Hyperfactorial array notation	6!	7!
X-Sequence Hyper-Exponential Notation	10{1}3
Steinhaus-Moser Notation	4[3]	5[3]
PlantStar's Debut Notation	[1]	[2]
H* function	H(-0.1)	H(-0)
Bashicu matrix system with respect to version 4	(0)[31]	(0)[32]
m(n) map	m(1)(4)	m(1)(5)
s(n) map	\(s(1)(\lambda x . x+1)(498)\)	\(s(1)(\lambda x . x+1)(499)\)