A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1189500 can be evenly divided by 1 2 3 4 5 6 10 12 13 15 20 25 26 30 39 50 52 60 61 65 75 78 100 122 125 130 150 156 183 195 244 250 260 300 305 325 366 375 390 500 610 650 732 750 780 793 915 975 1,220 1,300 1,500 1,525 1,586 1,625 1,830 1,950 2,379 3,050 3,172 3,250 3,660 3,900 3,965 4,575 4,758 4,875 6,100 6,500 7,625 7,930 9,150 9,516 9,750 11,895 15,250 15,860 18,300 19,500 19,825 22,875 23,790 30,500 39,650 45,750 47,580 59,475 79,300 91,500 99,125 118,950 198,250 237,900 297,375 396,500 594,750 and 1,189,500, with no remainder.
Since 1,189,500 cannot be divided by just 1 and 1,189,500, it is not a prime number.