A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3081240 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 18 20 24 27 30 36 40 45 54 60 72 81 90 108 120 135 162 180 216 243 270 317 324 360 405 486 540 634 648 810 951 972 1,080 1,215 1,268 1,585 1,620 1,902 1,944 2,430 2,536 2,853 3,170 3,240 3,804 4,755 4,860 5,706 6,340 7,608 8,559 9,510 9,720 11,412 12,680 14,265 17,118 19,020 22,824 25,677 28,530 34,236 38,040 42,795 51,354 57,060 68,472 77,031 85,590 102,708 114,120 128,385 154,062 171,180 205,416 256,770 308,124 342,360 385,155 513,540 616,248 770,310 1,027,080 1,540,620 and 3,081,240, with no remainder.
Since 3,081,240 cannot be divided by just 1 and 3,081,240, it is not a prime number.