A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 387600 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 19 20 24 25 30 34 38 40 48 50 51 57 60 68 75 76 80 85 95 100 102 114 120 136 150 152 170 190 200 204 228 240 255 272 285 300 304 323 340 380 400 408 425 456 475 510 570 600 646 680 760 816 850 912 950 969 1,020 1,140 1,200 1,275 1,292 1,360 1,425 1,520 1,615 1,700 1,900 1,938 2,040 2,280 2,550 2,584 2,850 3,230 3,400 3,800 3,876 4,080 4,560 4,845 5,100 5,168 5,700 6,460 6,800 7,600 7,752 8,075 9,690 10,200 11,400 12,920 15,504 16,150 19,380 20,400 22,800 24,225 25,840 32,300 38,760 48,450 64,600 77,520 96,900 129,200 193,800 and 387,600, with no remainder.
Since 387,600 cannot be divided by just 1 and 387,600, it is not a prime number.