A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3967488 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 27 28 32 36 41 42 48 54 56 63 64 72 82 84 96 108 112 123 126 128 144 164 168 189 192 216 224 246 252 256 287 288 328 336 369 378 384 432 448 492 504 512 574 576 656 672 738 756 768 861 864 896 984 1,008 1,107 1,148 1,152 1,312 1,344 1,476 1,512 1,536 1,722 1,728 1,792 1,968 2,016 2,214 2,296 2,304 2,583 2,624 2,688 2,952 3,024 3,444 3,456 3,584 3,936 4,032 4,428 4,592 4,608 5,166 5,248 5,376 5,904 6,048 6,888 6,912 7,749 7,872 8,064 8,856 9,184 10,332 10,496 10,752 11,808 12,096 13,776 13,824 15,498 15,744 16,128 17,712 18,368 20,664 20,992 23,616 24,192 27,552 30,996 31,488 32,256 35,424 36,736 41,328 47,232 48,384 55,104 61,992 62,976 70,848 73,472 82,656 94,464 96,768 110,208 123,984 141,696 146,944 165,312 188,928 220,416 247,968 283,392 330,624 440,832 495,936 566,784 661,248 991,872 1,322,496 1,983,744 and 3,967,488, with no remainder.
Since 3,967,488 cannot be divided by just 1 and 3,967,488, it is not a prime number.