A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3429240 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 17 20 24 30 34 40 41 51 60 68 82 85 102 120 123 136 164 170 204 205 246 255 328 340 408 410 492 510 615 680 697 820 984 1,020 1,230 1,394 1,640 1,681 2,040 2,091 2,460 2,788 3,362 3,485 4,182 4,920 5,043 5,576 6,724 6,970 8,364 8,405 10,086 10,455 13,448 13,940 16,728 16,810 20,172 20,910 25,215 27,880 28,577 33,620 40,344 41,820 50,430 57,154 67,240 83,640 85,731 100,860 114,308 142,885 171,462 201,720 228,616 285,770 342,924 428,655 571,540 685,848 857,310 1,143,080 1,714,620 and 3,429,240, with no remainder.
Since 3,429,240 cannot be divided by just 1 and 3,429,240, it is not a prime number.