A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5661600 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 16 20 21 24 25 28 30 32 35 40 42 48 50 56 60 70 75 80 84 96 100 105 112 120 140 150 160 168 175 200 210 224 240 280 300 336 337 350 400 420 480 525 560 600 672 674 700 800 840 1,011 1,050 1,120 1,200 1,348 1,400 1,680 1,685 2,022 2,100 2,359 2,400 2,696 2,800 3,360 3,370 4,044 4,200 4,718 5,055 5,392 5,600 6,740 7,077 8,088 8,400 8,425 9,436 10,110 10,784 11,795 13,480 14,154 16,176 16,800 16,850 18,872 20,220 23,590 25,275 26,960 28,308 32,352 33,700 35,385 37,744 40,440 47,180 50,550 53,920 56,616 58,975 67,400 70,770 75,488 80,880 94,360 101,100 113,232 117,950 134,800 141,540 161,760 176,925 188,720 202,200 226,464 235,900 269,600 283,080 353,850 377,440 404,400 471,800 566,160 707,700 808,800 943,600 1,132,320 1,415,400 1,887,200 2,830,800 and 5,661,600, with no remainder.
Since 5,661,600 cannot be divided by just 1 and 5,661,600, it is not a prime number.