A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2105600 can be evenly divided by 1 2 4 5 7 8 10 14 16 20 25 28 32 35 40 47 50 56 64 70 80 94 100 112 128 140 160 175 188 200 224 235 256 280 320 329 350 376 400 448 470 560 640 658 700 752 800 896 940 1,120 1,175 1,280 1,316 1,400 1,504 1,600 1,645 1,792 1,880 2,240 2,350 2,632 2,800 3,008 3,200 3,290 3,760 4,480 4,700 5,264 5,600 6,016 6,400 6,580 7,520 8,225 8,960 9,400 10,528 11,200 12,032 13,160 15,040 16,450 18,800 21,056 22,400 26,320 30,080 32,900 37,600 42,112 44,800 52,640 60,160 65,800 75,200 84,224 105,280 131,600 150,400 210,560 263,200 300,800 421,120 526,400 1,052,800 and 2,105,600, with no remainder.
Since 2,105,600 cannot be divided by just 1 and 2,105,600, it is not a prime number.