A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 336336 can be evenly divided by 1 2 3 4 6 7 8 11 12 13 14 16 21 22 24 26 28 33 39 42 44 48 49 52 56 66 77 78 84 88 91 98 104 112 132 143 147 154 156 168 176 182 196 208 231 264 273 286 294 308 312 336 364 392 429 462 528 539 546 572 588 616 624 637 728 784 858 924 1,001 1,078 1,092 1,144 1,176 1,232 1,274 1,456 1,617 1,716 1,848 1,911 2,002 2,156 2,184 2,288 2,352 2,548 3,003 3,234 3,432 3,696 3,822 4,004 4,312 4,368 5,096 6,006 6,468 6,864 7,007 7,644 8,008 8,624 10,192 12,012 12,936 14,014 15,288 16,016 21,021 24,024 25,872 28,028 30,576 42,042 48,048 56,056 84,084 112,112 168,168 and 336,336, with no remainder.
Since 336,336 cannot be divided by just 1 and 336,336, it is not a prime number.