回復 5# studentJ 的帖子
第 6 題
a_n 表示前進 n 步的方法數
a_1 = 1
a_2 = 2
a_3 = a_1 + a_2 + 1 = 4
a_4 = a_1 + a_2 + a_3 + 1 = 8
a_5 = a_1 + a_2 + a_3 + a_4 + 1 = 16
a_6 = a_1 + a_2 + a_3 + a_4 + a_5 + 1 = 32
a_7 = a_1 + a_2 + a_3 + a_4 + a_5 + a_6 = 63
a_8 = a_2 + a_3 + a_4 + a_5 + a_6 + a_7 = 125
a_9 = a_3 + a_4 + a_5 + a_6 + a_7 + a_8 = 248
a_10 = a_4 + a_5 + a_6 + a_7 + a_8 + a_9 = 492