A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3791760 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 16 20 21 24 28 30 35 37 40 42 48 56 60 61 70 74 80 84 105 111 112 120 122 140 148 168 183 185 210 222 240 244 259 280 296 305 336 366 370 420 427 444 488 518 555 560 592 610 732 740 777 840 854 888 915 976 1,036 1,110 1,220 1,281 1,295 1,464 1,480 1,554 1,680 1,708 1,776 1,830 2,072 2,135 2,220 2,257 2,440 2,562 2,590 2,928 2,960 3,108 3,416 3,660 3,885 4,144 4,270 4,440 4,514 4,880 5,124 5,180 6,216 6,405 6,771 6,832 7,320 7,770 8,540 8,880 9,028 10,248 10,360 11,285 12,432 12,810 13,542 14,640 15,540 15,799 17,080 18,056 20,496 20,720 22,570 25,620 27,084 31,080 31,598 33,855 34,160 36,112 45,140 47,397 51,240 54,168 62,160 63,196 67,710 78,995 90,280 94,794 102,480 108,336 126,392 135,420 157,990 180,560 189,588 236,985 252,784 270,840 315,980 379,176 473,970 541,680 631,960 758,352 947,940 1,263,920 1,895,880 and 3,791,760, with no remainder.
Since 3,791,760 cannot be divided by just 1 and 3,791,760, it is not a prime number.