Heptagonal

1 definition found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Heptagonal \Hep*tag"o*nal\, a. [Cf. F. heptagonal.]
     Having seven angles or sides.
     [1913 Webster]
  
     {Heptagonal numbers} (Arith.), the numbers of the series 1,
        7, 18, 34, 55, etc., being figurate numbers formed by


        adding successively the terms of the arithmetical series
        1, 6, 11, 16, 21, etc.
        [1913 Webster]