is the area and also the perimeter of a rectangle with 6 and 3unit sides. is the only number that is twice the sum of its digits.
= 3 + 4 + 5 + 6 (sum of consecutive numbers) = 3^{3}  3^{2} = (2 + 8)^{2}
18 _{=} 9 + 9 81 9 x 9
18^{3} = 5832 and 5 + 8 + 3 + 2 = 18
18^{3} = 5832 18^{4} = 104976 (both results together include all digits once)
18 equilateral triangles make a hexagon ring.
is the solution to the classic puzzle: "my age today is three times what it will be three years from now minus three times what my age was three years ago. How old am I?".
is a hate number symbol. The first letter of the alphabet is 'A'; the eighth letter of the alphabet is 'H'. Thus, 1 plus 8, or 18, equals 'AH', an abbreviation for Adolf Hitler. NeoNazis use 18 in tattoos. The number is also used by "Combat 18", a violent British neoNazi group that chose its name in honor of Adolf Hitler. The number 18 is also considered a number of the devil due to the fact that 6+6+6=18, and 666 is the Number of the Beast.
On Earth, the length of a day 900 million years ago was only about 18 hours.  Science magazine
Another interesting Finnish word that contains a sequence of 18 dots: Pääjäävääjää ('the main waiver' in Finnish, partitive case).  posted by Juhani Sirkiä 
The 18letter words 'conservationalists' and 'conversationalists' are anagrams of each other. They are the longest pair of anagrams with such properties.
There are 18 chapters in the Hindu epic tale Bhagavad Gita.
