heptagonal, a. (n.)
(hɛpˈtægənəl)
[f. heptagon + -al1: cf. F. heptagonale (1633 in Hatz.-Darm.).]
Having seven angles and seven sides.
heptagonal numbers, the series of polygonal numbers 1, 7, 18, 34, 55, 81, etc. formed by continuous summation of the arithmetical series 1, 6, 11, 16, 21, 26, etc.
| 1613 Selden in Drayton's Poly-olb. xi. (R.), In a circle describe an heptagonal and equilateral figure, from whose every side shall fall equilateral triangles. 1690 Leybourn Curs. Math. 279 It is called a Heptagonal Pyramide. 1796 Hutton Math. Dict. s.v., One property..of these Heptagonal numbers is, that if any one of them be multiplied by 40, and to the product add 9, the sum will be a square number. 1828 Stark Elem. Nat. Hist. I. 398 Body heptagonal, yellowish brown, variegated with narrow transverse deep brown bars. 1853 Ruskin Stones Ven. II. iii. §14. 37 We have therefore, externally a heptagonal apse. |
b. n. A heptagonal number.
| 1796 Hutton Math. Dict. s.v., The Heptagonals are formed by adding continually the terms of the arithmeticals. |