three

2

six

four

(9)(8) 12

( 16)。 . . . .

This series consists of two series.

1, 3, 5, 7, 9.。 . . . Numbers form a series, and the last number is twice that of the previous one.

2, 4, 6, 8, 10. . . . . Numbers form a series, which are 1 time, 2 times, 3 times, 4 times and 5 times 3. . . .