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A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number , other examples being square numbers and cube numbers . The n th triangular number is the number of dots in the triangular arrangement with n dots on each side, and is equal to the sum of the n natural ...
The Bell triangle, whose numbers count the partitions of a set in which a given element is the largest singleton [1] Catalan's triangle, which counts strings of matched parentheses [2] Euler's triangle, which counts permutations with a given number of ascents [3] Floyd's triangle, whose entries are all of the integers in order [4]
The Chisanbop system. When a finger is touching the table, it contributes its corresponding number to a total. Chisanbop or chisenbop (from Korean chi (ji) finger + sanpŏp (sanbeop) calculation [1] 지산법/指算法), sometimes called Fingermath, [2] is a finger counting method used to perform basic mathematical operations.
A collection of short problems and more talk of prime numbers: 1964 Jul: Curious properties of a cycloid curve 1964 Aug: Concerning several magic tricks based on mathematical principles 1964 Sep: Puns, palindromes and other word games that partake of the mathematical spirit 1964 Oct: Simple proofs of the Pythagorean theorem, and sundry other ...
One form of the mnemonic is done by counting on the knuckles of one's hand to remember the number of days in each month. [1] Knuckles are counted as 31 days, depressions between knuckles as 30 (or 28/29) days.
The apparent triangles formed from the figures are 13 units wide and 5 units tall, so it appears that the area should be S = 13×5 / 2 = 32.5 units. However, the blue triangle has a ratio of 5:2 (=2.5), while the red triangle has the ratio 8:3 (≈2.667), so the apparent combined hypotenuse in each figure is actually bent.
There is a method to construct all Pythagorean triples that contain a given positive integer x as one of the legs of the right-angled triangle associated with the triple. It means finding all right triangles whose sides have integer measures, with one leg predetermined as a given cathetus. [13] The formulas read as follows.
An example of a counting problem whose solution can be given in terms of the Narayana numbers (,), is the number of words containing pairs of parentheses, which are correctly matched (known as Dyck words) and which contain distinct nestings.