A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6442520 can be evenly divided by 1 2 4 5 7 8 10 14 19 20 28 35 38 40 49 56 70 76 95 98 133 140 152 173 190 196 245 266 280 346 380 392 490 532 665 692 760 865 931 980 1,064 1,211 1,330 1,384 1,730 1,862 1,960 2,422 2,660 3,287 3,460 3,724 4,655 4,844 5,320 6,055 6,574 6,920 7,448 8,477 9,310 9,688 12,110 13,148 16,435 16,954 18,620 23,009 24,220 26,296 32,870 33,908 37,240 42,385 46,018 48,440 65,740 67,816 84,770 92,036 115,045 131,480 161,063 169,540 184,072 230,090 322,126 339,080 460,180 644,252 805,315 920,360 1,288,504 1,610,630 3,221,260 and 6,442,520, with no remainder.
Since 6,442,520 cannot be divided by just 1 and 6,442,520, it is not a prime number.