A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 870048 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 19 24 27 32 36 38 48 53 54 57 72 76 96 106 108 114 144 152 159 171 212 216 228 288 304 318 342 424 432 456 477 513 608 636 684 848 864 912 954 1,007 1,026 1,272 1,368 1,431 1,696 1,824 1,908 2,014 2,052 2,544 2,736 2,862 3,021 3,816 4,028 4,104 5,088 5,472 5,724 6,042 7,632 8,056 8,208 9,063 11,448 12,084 15,264 16,112 16,416 18,126 22,896 24,168 27,189 32,224 36,252 45,792 48,336 54,378 72,504 96,672 108,756 145,008 217,512 290,016 435,024 and 870,048, with no remainder.
Since 870,048 cannot be divided by just 1 and 870,048, it is not a prime number.