A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1675440 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 13 15 16 18 20 24 26 30 36 39 40 45 48 52 60 65 72 78 80 90 104 117 120 130 144 156 179 180 195 208 234 240 260 312 358 360 390 468 520 537 585 624 716 720 780 895 936 1,040 1,074 1,170 1,432 1,560 1,611 1,790 1,872 2,148 2,327 2,340 2,685 2,864 3,120 3,222 3,580 4,296 4,654 4,680 5,370 6,444 6,981 7,160 8,055 8,592 9,308 9,360 10,740 11,635 12,888 13,962 14,320 16,110 18,616 20,943 21,480 23,270 25,776 27,924 32,220 34,905 37,232 41,886 42,960 46,540 55,848 64,440 69,810 83,772 93,080 104,715 111,696 128,880 139,620 167,544 186,160 209,430 279,240 335,088 418,860 558,480 837,720 and 1,675,440, with no remainder.
Since 1,675,440 cannot be divided by just 1 and 1,675,440, it is not a prime number.