nombres premiers (petite amusette)

3! = 6 3!/2 = 3 3

4!/3+1 = 9=3*3

5*8+1=41

6*40+1=241

7*240+1=41*41

8*1680+1=13441

9*13440+1= not prime

4! = 24 4!/2 = 12 3

5!/12+1 = 11

6*10+1 = 61

7*60 + 1= 421

8*420 + 1 = 3361

9*3360 +1= 30241

5!=120 120/2=60 3

6!/60+1=13

7*12+1=73

8*72+1=577

9*576+1=5*17*61

10*5184+1=47*1103

plus loin

10!/2 = 1814400 3

11!/1814400+1 = 23

12*22+1=265=5*53

13*264+1=3433

14*3432+1=48049

15*48048+1=not prime

plus loin

15!/2 = 653837184000=x

16!/653837184000+1=33=3*11

17*32+1=545=5*109

18*544+1=7*1399

19*9792+1=186049

20*186048+1= not prime