A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 4000640 can be evenly divided by 1 2 4 5 7 8 10 14 16 19 20 28 32 35 38 40 47 56 64 70 76 80 94 95 112 128 133 140 152 160 188 190 224 235 266 280 304 320 329 376 380 448 470 532 560 608 640 658 665 752 760 893 896 940 1,064 1,120 1,216 1,316 1,330 1,504 1,520 1,645 1,786 1,880 2,128 2,240 2,432 2,632 2,660 3,008 3,040 3,290 3,572 3,760 4,256 4,465 4,480 5,264 5,320 6,016 6,080 6,251 6,580 7,144 7,520 8,512 8,930 10,528 10,640 12,160 12,502 13,160 14,288 15,040 17,024 17,860 21,056 21,280 25,004 26,320 28,576 30,080 31,255 35,720 42,112 42,560 50,008 52,640 57,152 62,510 71,440 85,120 100,016 105,280 114,304 125,020 142,880 200,032 210,560 250,040 285,760 400,064 500,080 571,520 800,128 1,000,160 2,000,320 and 4,000,640, with no remainder.
Since 4,000,640 cannot be divided by just 1 and 4,000,640, it is not a prime number.