Abstract: A device and method for demonstrating number theory is disclosed in which the device comprises a frame consisting of the plurality of spaced parallel rods which are secured at their ends to transverse members. The rods carry slidable members which are arranged to define an triangle having the same number members on each side. The rods are spaced apart and the members are sized so that sliding movement of one bead will contact a bead located in the next adjacent rod and cause it to also slide. A member representing an ordinal number is selected and is moved along the rod to contact members adjacent to the selected member in the direction of movement to separate a sub-array of members from said equilateral triangle array. The selection of additional ordinal members contact with adjacent members is repeated so that depending upon the mathematical operation being demonstrated.