A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2151600 can be evenly divided by 1 2 3 4 5 6 8 10 11 12 15 16 20 22 24 25 30 33 40 44 48 50 55 60 66 75 80 88 100 110 120 132 150 163 165 176 200 220 240 264 275 300 326 330 400 440 489 528 550 600 652 660 815 825 880 978 1,100 1,200 1,304 1,320 1,630 1,650 1,793 1,956 2,200 2,445 2,608 2,640 3,260 3,300 3,586 3,912 4,075 4,400 4,890 5,379 6,520 6,600 7,172 7,824 8,150 8,965 9,780 10,758 12,225 13,040 13,200 14,344 16,300 17,930 19,560 21,516 24,450 26,895 28,688 32,600 35,860 39,120 43,032 44,825 48,900 53,790 65,200 71,720 86,064 89,650 97,800 107,580 134,475 143,440 179,300 195,600 215,160 268,950 358,600 430,320 537,900 717,200 1,075,800 and 2,151,600, with no remainder.
Since 2,151,600 cannot be divided by just 1 and 2,151,600, it is not a prime number.