: any of a progression of numbers formed from an arithmetical progression in which the first term is 1 and the difference an integer by taking the first term, and the sums of the first two, first three, first four, and so on as the successive terms of a new progression and by operating on this in the same way, and so on, the numbers in each sequence being such that points representing them are capable of arrangement in geometrical figures
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/fig"yeuhr it/, Math.
a number having the property that the same number of equally spaced dots can be arranged in the shape of a regular geometrical figure.
[1605-15]
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figurate number,
any one of the numbers occurring in a series that has been derived from an arithmetical progression whose first term is 1 and whose difference is a whole number. By taking for the consecutive terms of the derived series the first term, the sum of the first two terms, the sum of the first three terms, and so on, of the simple progression, the units of such a number can be arranged symmetrically in the form of a figure, as a triangle, characteristic of the series to which it belongs.
Useful english dictionary. 2012.