A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 975240 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 18 20 21 24 27 28 30 35 36 40 42 43 45 54 56 60 63 70 72 81 84 86 90 105 108 120 126 129 135 140 162 168 172 180 189 210 215 216 252 258 270 280 301 315 324 344 360 378 387 405 420 430 504 516 540 567 602 630 645 648 756 774 810 840 860 903 945 1,032 1,080 1,134 1,161 1,204 1,260 1,290 1,505 1,512 1,548 1,620 1,720 1,806 1,890 1,935 2,268 2,322 2,408 2,520 2,580 2,709 2,835 3,010 3,096 3,240 3,483 3,612 3,780 3,870 4,515 4,536 4,644 5,160 5,418 5,670 5,805 6,020 6,966 7,224 7,560 7,740 8,127 9,030 9,288 10,836 11,340 11,610 12,040 13,545 13,932 15,480 16,254 17,415 18,060 21,672 22,680 23,220 24,381 27,090 27,864 32,508 34,830 36,120 40,635 46,440 48,762 54,180 65,016 69,660 81,270 97,524 108,360 121,905 139,320 162,540 195,048 243,810 325,080 487,620 and 975,240, with no remainder.
Since 975,240 cannot be divided by just 1 and 975,240, it is not a prime number.