The number 770,640 can be evenly divided by 1 2 3 4 5 6 8 10 12 13 15 16 19 20 24 26 30 38 39 40 48 52 57 60 65 76 78 80 95 104 114 120 130 152 156 169 190 195 208 228 240 247 260 285 304 312 338 380 390 456 494 507 520 570 624 676 741 760 780 845 912 988 1,014 1,040 1,140 1,235 1,352 1,482 1,520 1,560 1,690 1,976 2,028 2,280 2,470 2,535 2,704 2,964 3,120 3,211 3,380 3,705 3,952 4,056 4,560 4,940 5,070 5,928 6,422 6,760 7,410 8,112 9,633 9,880 10,140 11,856 12,844 13,520 14,820 16,055 19,266 19,760 20,280 25,688 29,640 32,110 38,532 40,560 48,165 51,376 59,280 64,220 77,064 96,330 128,440 154,128 192,660 256,880 385,320 and 770,640, with no remainder.
Since 770,640 cannot be divided by just 1 and 770,640, it is a composite number.