A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2128680 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 73 81 90 108 120 135 146 162 180 216 219 243 270 292 324 360 365 405 438 486 540 584 648 657 729 730 810 876 972 1,080 1,095 1,215 1,314 1,458 1,460 1,620 1,752 1,944 1,971 2,190 2,430 2,628 2,916 2,920 3,240 3,285 3,645 3,942 4,380 4,860 5,256 5,832 5,913 6,570 7,290 7,884 8,760 9,720 9,855 11,826 13,140 14,580 15,768 17,739 19,710 23,652 26,280 29,160 29,565 35,478 39,420 47,304 53,217 59,130 70,956 78,840 88,695 106,434 118,260 141,912 177,390 212,868 236,520 266,085 354,780 425,736 532,170 709,560 1,064,340 and 2,128,680, with no remainder.
Since 2,128,680 cannot be divided by just 1 and 2,128,680, it is not a prime number.