"R" symbol for the set of real numbers in Microsoft Equation 3.0
to enter real numbers R (double-struck), complex numbers C, natural numbers N use \doubleR, \doubleC, \doubleN, etc. and press the space bar. This style is commonly known as double-struck.
The character ℝ can be found in the symbols list under the font Cambria Math in the Letterlike Subject set. I set an auto-correct option so that if I type $real
it will automatically insert this symbol.
in equation editor, type in \doubleR. (A shortcut to enter equation editor is ALT and +)