A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2560600 can be evenly divided by 1 2 4 5 7 8 10 14 20 25 28 31 35 40 50 56 59 62 70 100 118 124 140 155 175 200 217 236 248 280 295 310 350 413 434 472 590 620 700 775 826 868 1,085 1,180 1,240 1,400 1,475 1,550 1,652 1,736 1,829 2,065 2,170 2,360 2,950 3,100 3,304 3,658 4,130 4,340 5,425 5,900 6,200 7,316 8,260 8,680 9,145 10,325 10,850 11,800 12,803 14,632 16,520 18,290 20,650 21,700 25,606 36,580 41,300 43,400 45,725 51,212 64,015 73,160 82,600 91,450 102,424 128,030 182,900 256,060 320,075 365,800 512,120 640,150 1,280,300 and 2,560,600, with no remainder.
Since 2,560,600 cannot be divided by just 1 and 2,560,600, it is not a prime number.