A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1238760 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 18 20 24 27 30 31 36 37 40 45 54 60 62 72 74 90 93 108 111 120 124 135 148 155 180 185 186 216 222 248 270 279 296 310 333 360 370 372 444 465 540 555 558 620 666 740 744 837 888 930 999 1,080 1,110 1,116 1,147 1,240 1,332 1,395 1,480 1,665 1,674 1,860 1,998 2,220 2,232 2,294 2,664 2,790 3,330 3,348 3,441 3,720 3,996 4,185 4,440 4,588 4,995 5,580 5,735 6,660 6,696 6,882 7,992 8,370 9,176 9,990 10,323 11,160 11,470 13,320 13,764 16,740 17,205 19,980 20,646 22,940 27,528 30,969 33,480 34,410 39,960 41,292 45,880 51,615 61,938 68,820 82,584 103,230 123,876 137,640 154,845 206,460 247,752 309,690 412,920 619,380 and 1,238,760, with no remainder.
Since 1,238,760 cannot be divided by just 1 and 1,238,760, it is not a prime number.