Dabbaba

Dash

Data

Day of week

Decabolo

Decacube

Decadigital Identity

Decadigital Number

Decagon

Decagonal Centered Number 

Decagonal Gnomonic Number

Decagonal Hyperpyramidal Number

Decagonal Number

Decagonal Pyramidal Number

Decahedral Die

Decahex

Decahexaflexagon

Decanting

Deciamond

Decimal Notation

Decimation

Deciphering

Decoding  

Decomino

Decomposition

Decosceles

Deduction

Deductive Game

Deficient Number

Degree

Delambre Formula

Delian Problem

Delightful Lattice

Deltahedron

Denary Numeration

Dense Lattice

Density

Derangement

Descending Diagonal

Devi Calendar

Diabolic Cube

Diabolic Dominoes

Diabolic Doughnut

Diabolic Hypercube

Diabolic Square

Diabolo

Diagonal

Diagonal Graeco-Latin Square 

Diagonal Latin Square 

Diagonals

Diagram (1)

Diagram (2)

Diameter

Diametrical Number

Diamond (1)

Diamond (2)

Dichotomy

Dichromatic Map

Dicube

Die

Different Figure

Different Magic Square

Differentiation

Digimetic

Digit

Digitadition

Digit Anagram

Digital Fraction

Digital Identity

Digital Root

Digital Sum

Dihex

Dilated Number

Dimension

Diophantine Equation

Diophante Quadruple  

Diophantus' Epitaph

Dirichlet's Box Principle

Disappearance

Disappearing  Triangle

Discordant Permutation

Discubed Number

Disenchanted Square

Dispersion

Displacement

Distortion

Distribution by Room

Divine Proportion

Divisibility Tests

Division

Divisor

Dodecagon

Dodecahedral Die

Dodecahedral Number

Dodecahedron

Domination

Domino

Dominoes

Donut (1)

Donut (2)

Doors

Dot Paper

Double

Double-Barrier

Double-n

Double-Nine

Double-Six

Double or Quits

Double Torus

Doubly Magic Square

Dragon

Draughts

Drawers Principle

Drunkard's Walk

Dual

Dudeney Bowling

Dudeney Pentagon

Dürer's Magic Square