A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 710640 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 16 18 20 21 24 27 28 30 35 36 40 42 45 47 48 54 56 60 63 70 72 80 84 90 94 105 108 112 120 126 135 140 141 144 168 180 188 189 210 216 235 240 252 270 280 282 315 329 336 360 376 378 420 423 432 470 504 540 560 564 630 658 705 720 752 756 840 846 940 945 987 1,008 1,080 1,128 1,260 1,269 1,316 1,410 1,512 1,645 1,680 1,692 1,880 1,890 1,974 2,115 2,160 2,256 2,520 2,538 2,632 2,820 2,961 3,024 3,290 3,384 3,760 3,780 3,948 4,230 4,935 5,040 5,076 5,264 5,640 5,922 6,345 6,580 6,768 7,560 7,896 8,460 8,883 9,870 10,152 11,280 11,844 12,690 13,160 14,805 15,120 15,792 16,920 17,766 19,740 20,304 23,688 25,380 26,320 29,610 33,840 35,532 39,480 44,415 47,376 50,760 59,220 71,064 78,960 88,830 101,520 118,440 142,128 177,660 236,880 355,320 and 710,640, with no remainder.
Since 710,640 cannot be divided by just 1 and 710,640, it is not a prime number.