The 
th
Pontryagin class of a vector bundle is 
times the 
th Chern class of the complexification
of the vector bundle. It is also in the 
th cohomology group of the base space
involved.
Pontryagin Class
See also
Chern Class, Stiefel-Whitney ClassExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Pontryagin Class." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PontryaginClass.html