Blackboard Bold Font required

You just need to get the font Cambria Math from a Windows machine.

http://www.microsoft.com/typography/fonts/family.aspx?FID=360

Try Google-ing "Blackboard Bold free font"

:o)

Martin --

This is from Wikipedia:

+Blackboard bold is a typeface style that is often used for certain symbols in mathematical texts, in which certain lines of the symbol (usually vertical, or near-vertical lines) are doubled. The symbols usually denote number sets. Blackboard bold symbols are also referred to as double struck, although they cannot actually be produced by double striking on a typewriter. In some texts these symbols are simply shown in bold; blackboard bold in fact originated from the attempt to write bold letters on blackboards in a way that clearly differentiated them from non-bold letters.+

If you're looking for an outline font that looks like the letters in your example, you might want to go to Myfonts.com of Fonts.com and search for outline fonts.

Tom G. does not make mistakes.
Just so you know.

You mean like this?
http://www.free-fonts.com/font/blackboard_bold.html