A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1239750 can be evenly divided by 1 2 3 5 6 9 10 15 18 19 25 29 30 38 45 50 57 58 75 87 90 95 114 125 145 150 171 174 190 225 250 261 285 290 342 375 435 450 475 522 551 570 725 750 855 870 950 1,102 1,125 1,305 1,425 1,450 1,653 1,710 2,175 2,250 2,375 2,610 2,755 2,850 3,306 3,625 4,275 4,350 4,750 4,959 5,510 6,525 7,125 7,250 8,265 8,550 9,918 10,875 13,050 13,775 14,250 16,530 21,375 21,750 24,795 27,550 32,625 41,325 42,750 49,590 65,250 68,875 82,650 123,975 137,750 206,625 247,950 413,250 619,875 and 1,239,750, with no remainder.
Since 1,239,750 cannot be divided by just 1 and 1,239,750, it is not a prime number.