Your math is off. You tried to calculate the odds that the next block would collide you want the odds that any of them would collide.  <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Birthday_problem" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Birthday_problem</a><p>X!&#x2F;((X^n) * (X-n)!)<p>It only takes 23 people to have a 50&#x2F;50 shot of sharing a birthday.<p>On the plus side MD5 is 128bits.