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.

Homepage:
https://ctan.org/pkg/doublestroke
