A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6846240 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 20 24 30 32 34 40 48 51 60 68 80 85 96 102 120 136 160 170 204 240 255 272 340 408 480 510 544 680 816 839 1,020 1,360 1,632 1,678 2,040 2,517 2,720 3,356 4,080 4,195 5,034 6,712 8,160 8,390 10,068 12,585 13,424 14,263 16,780 20,136 25,170 26,848 28,526 33,560 40,272 42,789 50,340 57,052 67,120 71,315 80,544 85,578 100,680 114,104 134,240 142,630 171,156 201,360 213,945 228,208 285,260 342,312 402,720 427,890 456,416 570,520 684,624 855,780 1,141,040 1,369,248 1,711,560 2,282,080 3,423,120 and 6,846,240, with no remainder.
Since 6,846,240 cannot be divided by just 1 and 6,846,240, it is not a prime number.