MathDB
Sequence of Polyhedra

Source:

December 28, 2006
geometry3D geometrytetrahedronnumber theoryrelatively prime

Problem Statement

Given a triangle, its midpoint triangle is obtained by joining the midpoints of its sides. A sequence of polyhedra PiP_{i} is defined recursively as follows: P0P_{0} is a regular tetrahedron whose volume is 1. To obtain Pi+1P_{i+1}, replace the midpoint triangle of every face of PiP_{i} by an outward-pointing regular tetrahedron that has the midpoint triangle as a face. The volume of P3P_{3} is mn\frac{m}{n}, where mm and nn are relatively prime positive integers. Find m+nm+n.