A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2135880 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 17 18 20 24 30 34 36 40 45 51 60 68 72 85 90 102 120 136 153 170 180 204 255 306 340 349 360 408 510 612 680 698 765 1,020 1,047 1,224 1,396 1,530 1,745 2,040 2,094 2,792 3,060 3,141 3,490 4,188 5,235 5,933 6,120 6,282 6,980 8,376 10,470 11,866 12,564 13,960 15,705 17,799 20,940 23,732 25,128 29,665 31,410 35,598 41,880 47,464 53,397 59,330 62,820 71,196 88,995 106,794 118,660 125,640 142,392 177,990 213,588 237,320 266,985 355,980 427,176 533,970 711,960 1,067,940 and 2,135,880, with no remainder.
Since 2,135,880 cannot be divided by just 1 and 2,135,880, it is not a prime number.