Triangular numbers are of the form n*(n+1)/2. “One (1) is a positive integer one more than 0 and one less than 2. One is the only positive... 1 “Three (3) is a positive integer one more than 2 and one less than 4. Three is the 2nd prime... 3 “Six (6) is a positive integer one more than 5 and one less than 7. 6 is the second composite... 6 “Ten (10) is a positive integer one more than 9 and one less than 11. 10 is the base of our... 10 “A triangular number is a positive integer of the form n*(n+1)/2 where n is a positive integer... Triangular number “Fifteen (15) is a positive integer one more than 14 and one less than 16. 15 is the second odd... 15 “Twenty-one (21) is a positive integer one more than 20 and one less than 22. Properties 21 is a... 21 Pages in category "Triangular numbers" The following 7 pages are in this category, out of 7 total. 1 1 10 15 2 213 36 6 T Triangular number Categories: Numbers Add category Cancel Save