A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6790784 can be evenly divided by 1 2 4 7 8 11 13 14 16 22 26 28 32 44 52 53 56 64 77 88 91 104 106 112 128 143 154 176 182 208 212 224 286 308 352 364 371 416 424 448 572 583 616 689 704 728 742 832 848 896 1,001 1,144 1,166 1,232 1,378 1,408 1,456 1,484 1,664 1,696 2,002 2,288 2,332 2,464 2,756 2,912 2,968 3,392 4,004 4,081 4,576 4,664 4,823 4,928 5,512 5,824 5,936 6,784 7,579 8,008 8,162 9,152 9,328 9,646 9,856 11,024 11,648 11,872 15,158 16,016 16,324 18,304 18,656 19,292 22,048 23,744 30,316 32,032 32,648 37,312 38,584 44,096 47,488 53,053 60,632 64,064 65,296 74,624 77,168 88,192 106,106 121,264 128,128 130,592 154,336 212,212 242,528 261,184 308,672 424,424 485,056 522,368 617,344 848,848 970,112 1,697,696 3,395,392 and 6,790,784, with no remainder.
Since 6,790,784 cannot be divided by just 1 and 6,790,784, it is not a prime number.