A: The preferred answer is "Countdown (three tones of Tao) (four tones of Shu)". Because the order of natural number counting and queuing is 1234567, and this puzzle 765432 1 is "the number to the fourth tone (the third tone)", although "reciprocal"

The tone is different from Tao Shu, but the writing is the same.

As far as "mathematical nouns" are concerned, other answers are: arithmetic progression; Decreasing; In the reverse order.