A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 677280 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 20 24 30 32 34 40 48 51 60 68 80 83 85 96 102 120 136 160 166 170 204 240 249 255 272 332 340 408 415 480 498 510 544 664 680 816 830 996 1,020 1,245 1,328 1,360 1,411 1,632 1,660 1,992 2,040 2,490 2,656 2,720 2,822 3,320 3,984 4,080 4,233 4,980 5,644 6,640 7,055 7,968 8,160 8,466 9,960 11,288 13,280 14,110 16,932 19,920 21,165 22,576 28,220 33,864 39,840 42,330 45,152 56,440 67,728 84,660 112,880 135,456 169,320 225,760 338,640 and 677,280, with no remainder.
Since 677,280 cannot be divided by just 1 and 677,280, it is not a prime number.