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Is it possible to find $n>1$ such that $\mathbb{R}P^{2n+1}$ doesn't have smooth non vanishing vector field? I know it is not true for $S^{2n+1} \ $ and $ \ \mathbb{R}P^{2n+1}$ is a sphere modulo antipod map, but I cannot see the answer thanks.

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    $\begingroup$ The usual examples of smooth non-vanishing vector fields on odd-dimensional spheres seem to be invariant under the antipodal map so they descend to the projective space. $\endgroup$ – Andreas Blass Jan 9 '13 at 19:09
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In the proof of Poincare-Hopf theorem, we see that a compact smooth manifold have a non-vanishing smooth tangent vector field if and only if it's Euler Character is $0$. And it's easy to prove that every odd-dimensional compact smooth manifold must have Euler Character $0$.

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  • $\begingroup$ That theorem doesn't work with $\mathbb{R}P^{2n+1}$, which is NOT orientable $\endgroup$ – avati91 Oct 8 '15 at 16:22
  • $\begingroup$ I'm not an expert in topology, but if my memory was right, they ARE orientable... $\endgroup$ – lee Nov 3 '15 at 18:42

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