1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ..... 2 2 2 2 2 2 2 2 2 2 ..... 3 3 3 3 3 ..... 4 4 ..... 5 .....------------------------------------------------1 2 1 3 1 2 1 4 1 2 1 3 1 2 1 5 1 2 1 3 ......(求此数列的通项)