a_0=a_1=1\ ,\ \ a_n=a_{n-1}+(n-1)a_{n-2}\ \ \ (n\ge2)
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Recent Referers:
  1. http://formula.s21g.com/?a_0%3Da_1%3D1%5C%20,%5C%20%5C%20...
  2. http://formula.s21g.com/
  3. http://blog.s21g.com/articles/2012.8
  4. http://blog.s21g.com/?page=7
  5. http://blog.s21g.com/lvs?page=1