The number 6,345,216 can be evenly divided by 1 2 3 4 6 8 9 12 16 17 18 24 27 32 34 36 48 51 54 64 68 72 81 96 102 108 128 136 144 153 162 192 204 216 243 256 272 288 306 324 384 408 432 459 486 512 544 576 612 648 729 768 816 864 918 972 1,088 1,152 1,224 1,296 1,377 1,458 1,536 1,632 1,728 1,836 1,944 2,176 2,304 2,448 2,592 2,754 2,916 3,264 3,456 3,672 3,888 4,131 4,352 4,608 4,896 5,184 5,508 5,832 6,528 6,912 7,344 7,776 8,262 8,704 9,792 10,368 11,016 11,664 12,393 13,056 13,824 14,688 15,552 16,524 19,584 20,736 22,032 23,328 24,786 26,112 29,376 31,104 33,048 39,168 41,472 44,064 46,656 49,572 58,752 62,208 66,096 78,336 88,128 93,312 99,144 117,504 124,416 132,192 176,256 186,624 198,288 235,008 264,384 352,512 373,248 396,576 528,768 705,024 793,152 1,057,536 1,586,304 2,115,072 3,172,608 and 6,345,216, with no remainder.
Since 6,345,216 cannot be divided by just 1 and 6,345,216, it is a composite number.