A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 709280 can be evenly divided by 1 2 4 5 8 10 11 13 16 20 22 26 31 32 40 44 52 55 62 65 80 88 104 110 124 130 143 155 160 176 208 220 248 260 286 310 341 352 403 416 440 496 520 572 620 682 715 806 880 992 1,040 1,144 1,240 1,364 1,430 1,612 1,705 1,760 2,015 2,080 2,288 2,480 2,728 2,860 3,224 3,410 4,030 4,433 4,576 4,960 5,456 5,720 6,448 6,820 8,060 8,866 10,912 11,440 12,896 13,640 16,120 17,732 22,165 22,880 27,280 32,240 35,464 44,330 54,560 64,480 70,928 88,660 141,856 177,320 354,640 and 709,280, with no remainder.
Since 709,280 cannot be divided by just 1 and 709,280, it is not a prime number.