A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 205200 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 18 19 20 24 25 27 30 36 38 40 45 48 50 54 57 60 72 75 76 80 90 95 100 108 114 120 135 144 150 152 171 180 190 200 216 225 228 240 270 285 300 304 342 360 380 400 432 450 456 475 513 540 570 600 675 684 720 760 855 900 912 950 1,026 1,080 1,140 1,200 1,350 1,368 1,425 1,520 1,710 1,800 1,900 2,052 2,160 2,280 2,565 2,700 2,736 2,850 3,420 3,600 3,800 4,104 4,275 4,560 5,130 5,400 5,700 6,840 7,600 8,208 8,550 10,260 10,800 11,400 12,825 13,680 17,100 20,520 22,800 25,650 34,200 41,040 51,300 68,400 102,600 and 205,200, with no remainder.
Since 205,200 cannot be divided by just 1 and 205,200, it is not a prime number.