A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1396560 can be evenly divided by 1 2 3 4 5 6 8 10 11 12 15 16 20 22 23 24 30 33 40 44 46 48 55 60 66 69 80 88 92 110 115 120 132 138 165 176 184 220 230 240 253 264 276 330 345 368 440 460 506 528 529 552 660 690 759 880 920 1,012 1,058 1,104 1,265 1,320 1,380 1,518 1,587 1,840 2,024 2,116 2,530 2,640 2,645 2,760 3,036 3,174 3,795 4,048 4,232 5,060 5,290 5,520 5,819 6,072 6,348 7,590 7,935 8,464 10,120 10,580 11,638 12,144 12,696 15,180 15,870 17,457 20,240 21,160 23,276 25,392 29,095 30,360 31,740 34,914 42,320 46,552 58,190 60,720 63,480 69,828 87,285 93,104 116,380 126,960 139,656 174,570 232,760 279,312 349,140 465,520 698,280 and 1,396,560, with no remainder.
Since 1,396,560 cannot be divided by just 1 and 1,396,560, it is not a prime number.