The number 642,600 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 17 18 20 21 24 25 27 28 30 34 35 36 40 42 45 50 51 54 56 60 63 68 70 72 75 84 85 90 100 102 105 108 119 120 126 135 136 140 150 153 168 170 175 180 189 200 204 210 216 225 238 252 255 270 280 300 306 315 340 350 357 360 378 408 420 425 450 459 476 504 510 525 540 595 600 612 630 675 680 700 714 756 765 840 850 900 918 945 952 1,020 1,050 1,071 1,080 1,190 1,224 1,260 1,275 1,350 1,400 1,428 1,512 1,530 1,575 1,700 1,785 1,800 1,836 1,890 2,040 2,100 2,142 2,295 2,380 2,520 2,550 2,700 2,856 2,975 3,060 3,150 3,213 3,400 3,570 3,672 3,780 3,825 4,200 4,284 4,590 4,725 4,760 5,100 5,355 5,400 5,950 6,120 6,300 6,426 7,140 7,560 7,650 8,568 8,925 9,180 9,450 10,200 10,710 11,475 11,900 12,600 12,852 14,280 15,300 16,065 17,850 18,360 18,900 21,420 22,950 23,800 25,704 26,775 30,600 32,130 35,700 37,800 42,840 45,900 53,550 64,260 71,400 80,325 91,800 107,100 128,520 160,650 214,200 321,300 and 642,600, with no remainder.
Since 642,600 cannot be divided by just 1 and 642,600, it is a composite number.