A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 996360 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 19 20 23 24 30 38 40 46 57 60 69 76 92 95 114 115 120 138 152 184 190 228 230 276 285 345 361 380 437 456 460 552 570 690 722 760 874 920 1,083 1,140 1,311 1,380 1,444 1,748 1,805 2,166 2,185 2,280 2,622 2,760 2,888 3,496 3,610 4,332 4,370 5,244 5,415 6,555 7,220 8,303 8,664 8,740 10,488 10,830 13,110 14,440 16,606 17,480 21,660 24,909 26,220 33,212 41,515 43,320 49,818 52,440 66,424 83,030 99,636 124,545 166,060 199,272 249,090 332,120 498,180 and 996,360, with no remainder.
Since 996,360 cannot be divided by just 1 and 996,360, it is not a prime number.