How to quickly insert Double strike or Blackboard bold symbols in Word equations

To type the symbols in Double strike or Blackboard bold in the equation Microsoft Word (to insert equation into your text, click Alt+=), do one of the following:

• Under Equation Tools, on the Design tab, in the Symbols group, click the More button:
  

  In the top of list of symbols choose Scripts:

  

  In the Scripts list, in the Double-Struck group, choose the symbol you prefer:

• Type \double + capital or lowercase letter:

Capital letters in the Double strike or Blackboard bold:

Symbol	Code	Description
	\doubleA	Represents the algebraic numbers or affine space in algebraic geometry. Occasionally represents the algebraic numbers, the algebraic closure of ℚ (more commonly written or ), or the algebraic integers, an important subring of the algebraic numbers.
	\doubleB	Sometimes represents a ball, a Boolean domain, or the Brauer group of a field.
	\doubleC	Represents the set of complex numbers.
	\doubleD	Represents the unit (open) disk in the complex plane (and by generalisation 𝔻n may mean the n-dimensional ball) — for example as a model of the Hyperbolic plane. Occasionally 𝔻 may mean the decimal fractions (see number) or split-complex numbers.
	\doubleE	Represents the expected value of a random variable, or Euclidean space, or a field in a tower of fields, or the Eudoxus reals.
	\doubleF	Represents a field. Often used for finite fields, with a subscript to indicate the order. Also represents a Hirzebruch surface or a free group, with a subset to indicate the number of generators (or generating set, if infinite).
	\doubleG	Represents a Grassmannian or a group, especially an algebraic group.
	\doubleH	Represents the quaternions (the H stands for Hamilton), or the upper half-plane, or hyperbolic space, or hyperhomology of a complex.
	\doubleI	The closed unit interval or the ideal of polynomials vanishing on a subset. Occasionally the identity mapping on an algebraic structure, or an indicator function, or the set of imaginary numbers (i.e., the set of all real multiples of the imaginary unit, more commonly indicated i ℝ).
	\doubleJ	Occasionally represents the set of irrational numbers, R\Q (ℝ\ℚ).
	\doubleK	Represents a field, typically a scalar field. This is derived from the German word Körper, which is German for field (literally, "body"; cf. the French term corps). May also be used to denote a compact space.
	\doubleL	Represents the Lefschetz motive.
	\doubleM	Sometimes represents the monster group. The set of all m-by-n matrices is sometimes denoted 𝕄(m, n).
	\doubleN	Blackboard bold capital N (for natural numbers set).
	\doubleO	Represents the octonions.
	\doubleP	Represents projective space, the probability of an event, the prime numbers, a power set, the irrational numbers, or a forcing poset.
	\doubleQ	Blackboard bold capital Q (for rational numbers set).
	\doubleR	Represents the set of real numbers. ℝ>0 represents the positive reals, while ℝ≥0 represents the non-negative real numbers.
	\doubleS	Represents a sphere, or the sphere spectrum, or occasionally the sedenions.
	\doubleT	Represents the circle group, particularly the unit circle in the complex plane (and 𝕋n the n-dimensional torus), or a Hecke algebra (Hecke denoted his operators as Tn or 𝕋ℕ), or the tropical semi-ring, or twistor space.
	\doubleU
	\doubleV	Represents a vector space or an affine variety generated by a set of polynomials.
	\doubleW	Occasionally represents the set of whole numbers (here in the sense of non-negative integers), which also are represented by ℕ0.
	\doubleX	Occasionally used to denote an arbitrary metric space.
	\doubleY
	\doubleZ	Represents the set of integers.

Some lowercase letters in the Double strike or Blackboard bold:

Symbol	Code	Description
	\doublea
	\doubleb
	\doublec
	\doubled	May represent the differential symbol.
	\doublee	Occasionally used for the mathematical constant e.
	\doublef
	\doubleg
	\doubleh
	\doublei	Occasionally used for the imaginary unit.
	\doublej

See also this tip in French: Comment insérer rapidement des symboles double barre ou blackboard gras dans l'équation Word.