\magnification=1200 \parindent=0cm

\font\sixrm=ec-lmr10 at 6pt
\font\fourrm=ec-lmr10 at 4pt
\font\threerm=ec-lmr10 at 3pt

\def\bDelta{{\mathchoice
    {\Delta\rlap{\kern-6.4pt\raise1.8pt\hbox{\sixrm/}}}
    {\Delta\rlap{\kern-6.4pt\raise1.8pt\hbox{\sixrm/}}}    
    {\Delta\rlap{\kern-4.9pt\raise1pt\hbox{\fourrm/}}}
    {\Delta\rlap{\kern-4pt\raise1pt\hbox{\threerm/}}}}}    

Ceci est une formule centrée
$$\bDelta,$$
et, en ligne, $\bDelta$, $\int_\bDelta$, $\int_{A_\bDelta}$.

\end