A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2805920 can be evenly divided by 1 2 4 5 8 10 13 16 19 20 26 32 38 40 52 65 71 76 80 95 104 130 142 152 160 190 208 247 260 284 304 355 380 416 494 520 568 608 710 760 923 988 1,040 1,136 1,235 1,349 1,420 1,520 1,846 1,976 2,080 2,272 2,470 2,698 2,840 3,040 3,692 3,952 4,615 4,940 5,396 5,680 6,745 7,384 7,904 9,230 9,880 10,792 11,360 13,490 14,768 17,537 18,460 19,760 21,584 26,980 29,536 35,074 36,920 39,520 43,168 53,960 70,148 73,840 87,685 107,920 140,296 147,680 175,370 215,840 280,592 350,740 561,184 701,480 1,402,960 and 2,805,920, with no remainder.
Since 2,805,920 cannot be divided by just 1 and 2,805,920, it is not a prime number.