A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3042780 can be evenly divided by 1 2 3 4 5 6 10 12 13 15 20 26 30 39 47 52 60 65 78 83 94 130 141 156 166 188 195 235 249 260 282 332 390 415 470 498 564 611 705 780 830 940 996 1,079 1,222 1,245 1,410 1,660 1,833 2,158 2,444 2,490 2,820 3,055 3,237 3,666 3,901 4,316 4,980 5,395 6,110 6,474 7,332 7,802 9,165 10,790 11,703 12,220 12,948 15,604 16,185 18,330 19,505 21,580 23,406 32,370 36,660 39,010 46,812 50,713 58,515 64,740 78,020 101,426 117,030 152,139 202,852 234,060 253,565 304,278 507,130 608,556 760,695 1,014,260 1,521,390 and 3,042,780, with no remainder.
Since 3,042,780 cannot be divided by just 1 and 3,042,780, it is not a prime number.