A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 354816 can be evenly divided by 1 2 3 4 6 7 8 9 11 12 14 16 18 21 22 24 28 32 33 36 42 44 48 56 63 64 66 72 77 84 88 96 99 112 126 128 132 144 154 168 176 192 198 224 231 252 256 264 288 308 336 352 384 396 448 462 504 512 528 576 616 672 693 704 768 792 896 924 1,008 1,056 1,152 1,232 1,344 1,386 1,408 1,536 1,584 1,792 1,848 2,016 2,112 2,304 2,464 2,688 2,772 2,816 3,168 3,584 3,696 4,032 4,224 4,608 4,928 5,376 5,544 5,632 6,336 7,392 8,064 8,448 9,856 10,752 11,088 12,672 14,784 16,128 16,896 19,712 22,176 25,344 29,568 32,256 39,424 44,352 50,688 59,136 88,704 118,272 177,408 and 354,816, with no remainder.
Since 354,816 cannot be divided by just 1 and 354,816, it is not a prime number.