HEPTAGON

(Yunanca köken — orijinale bakınız.) In Geometry, a plane figure of seven sides. The area of a regular heptagon is equal to the square of one of its sides mulrWied into the constant number 3-6330124, or seven fourths of the taneent of the angle at the base to radius 1. I I KIT AGONAL NUMBERS, are a kind of polygonal numbers, of which the difference of the terms of the corresponding arithmetical progre ion is 5. Thus, Arithmetic als.. 1, 6, 11, 16, 21, .; Heptngonals.... 1, 7, 18, 34, 55, .; the latter being formed by the continual addition of the terms of the first. Among other properties of heptagonal numbers there is one very remarkable; namely, that if any heptagonal number is multiplied by 40, and 9 added to the product, the sum is a square number. [s. 567]