13!/(2!2!2!2!)-4*12!/(2!2!2!)+6*11!/(2!2!)-4*10!/2!+9!

來源: 2009-11-05 13:53:05 [舊帖] [給我悄悄話] 本文已被閱讀:

same reasoning as 惡狼, slightly different coefficients.