CTAN upload: doublestroke font
doublestroke – Typeset mathematical double stroke symbols
A font based on Computer Modern Roman useful for typesetting the mathematical symbols for the natural numbers (N), whole numbers (Z), rational numbers (Q), real numbers (R) and complex numbers (C); coverage includes all Roman capital letters, ‘1’, ‘h’ and ‘k’. The font is available both as METAFONT source and in Adobe Type 1 format, and LaTeX macros for its use are provided.
The fonts appear in the blackboard bold sampler.