Here is the mathematical proof the seventh day is the Sabbath day:

(1 x 2 x 3 ) x ( 4 x 5 x 6 ) : ( 8 x 9 x 10 ) =

1
If you are not totally convinced, this one must eliminate any silly doubt:

(1 + 2 + 3 + 4 + 5 + 6) + (8 + 9 + 10 + 11 + 12)

= 21 + 27

= 48

= theseventhdaylack

> and

7

^{2} minus theseventhdaylack =

1
Math is fun!