A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3412920 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 17 20 21 24 28 30 34 35 40 42 51 56 60 68 70 84 85 102 105 119 120 136 140 168 170 204 210 238 239 255 280 340 357 408 420 476 478 510 595 680 714 717 840 952 956 1,020 1,190 1,195 1,428 1,434 1,673 1,785 1,912 2,040 2,380 2,390 2,856 2,868 3,346 3,570 3,585 4,063 4,760 4,780 5,019 5,736 6,692 7,140 7,170 8,126 8,365 9,560 10,038 12,189 13,384 14,280 14,340 16,252 16,730 20,076 20,315 24,378 25,095 28,441 28,680 32,504 33,460 40,152 40,630 48,756 50,190 56,882 60,945 66,920 81,260 85,323 97,512 100,380 113,764 121,890 142,205 162,520 170,646 200,760 227,528 243,780 284,410 341,292 426,615 487,560 568,820 682,584 853,230 1,137,640 1,706,460 and 3,412,920, with no remainder.
Since 3,412,920 cannot be divided by just 1 and 3,412,920, it is not a prime number.