Pentacube Oddities with Dual Diagonal Box Symmetry

Introduction

A pentacube is a solid made of five cubes joined face to face. An oddity (or Sillke Figure) is a figure with even symmetry formed by an odd number of copies of a polyform.

Polycubes have 33 symmetry classes (including asymmetry), and 31 of them have even order. Here I show oddities with mirror symmetry through two diagonal planes and across the axis of their intersection. In all pictures, the cross-sections are shown from top to bottom. If you find a smaller solution, please write.

For other classes of symmetry, see Polycube Oddities.

Nomenclature

Dual Diagonal Box Symmetry

Dual diagonal box symmetry (Lunnon EFF7) is the symmetry of reflection through the planes x + y = 0, x − y = 0, and z = 0.

The smallest example of a polycube with dual diagonal box symmetry and no stronger symmetry is this heptacube (7-cube), as found by W. F. Lunnon:

Achiral Pentacubes

The solutions for pentacubes I and X are trivial. Those pentacubes already have dual diagonal box symmetry.

The solution for pentacube A has full symmetry. No smaller solution is known.

The solutions for pentacubes N, W, X, and Y are polycube equivalents of the smallest known dual diagonal oddities for the corresponding pentominoes. No smaller solutions are known.

Chiral, Disallowing Reflection

Chiral, Allowing Reflection

Last revised 2026-10-29.


Back to Polycube Oddities < Polyform Oddities < Polyform Curiosities
Col. George Sicherman [ HOME | MAIL ]