'Pyramidal numbers' definitions:

Definition of 'Pyramidal numbers'

From: GCIDE
  • Pyramidal \Py*ram`i*dal\, a. [Cf. F. pyramidal.] [1913 Webster]
  • 1. Of or pertaining to a pyramid; in the form of a a pyramid; pyramidical; as, pyramidal cleavage. [1913 Webster]
  • The mystic obelisks stand up Triangular, pyramidal. --Mrs. Browning. [1913 Webster]
  • 2. (Crystallog.) Same as Tetragonal. [1913 Webster]
  • Pyramidal numbers (Math.), certain series of figurate numbers expressing the number of balls or points that may be arranged in the form of pyramids. Thus 1, 4, 10, 20,
  • 35, etc., are triangular pyramidal numbers; and 1, 5, 14,
  • 30, 55, etc., are square pyramidal numbers. [1913 Webster]