12 Days of Christmas
Side to the Modius strip
The only self-hyperoperand
Triangular platonic solid
Necessary map colours
Exceptional lie group
The smallest perfect number
Frieze groups
Basis vectors of the octanians
Heegner numbers
Vertices of the Petersen graph
Coordinate systems in which the Helmholtz equation is separable
The reciprocal of -(1+2+3+4+...)