A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3177720 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 13 14 15 18 20 21 24 26 28 30 35 36 39 40 42 45 52 56 60 63 65 70 72 78 84 90 91 97 104 105 117 120 126 130 140 156 168 180 182 194 195 210 234 252 260 273 280 291 312 315 360 364 388 390 420 455 468 485 504 520 546 582 585 630 679 728 776 780 819 840 873 910 936 970 1,092 1,164 1,170 1,260 1,261 1,358 1,365 1,455 1,560 1,638 1,746 1,820 1,940 2,037 2,184 2,328 2,340 2,520 2,522 2,716 2,730 2,910 3,276 3,395 3,492 3,640 3,783 3,880 4,074 4,095 4,365 4,680 5,044 5,432 5,460 5,820 6,111 6,305 6,552 6,790 6,984 7,566 8,148 8,190 8,730 8,827 10,088 10,185 10,920 11,349 11,640 12,222 12,610 13,580 15,132 16,296 16,380 17,460 17,654 18,915 20,370 22,698 24,444 25,220 26,481 27,160 30,264 30,555 32,760 34,920 35,308 37,830 40,740 44,135 45,396 48,888 50,440 52,962 56,745 61,110 70,616 75,660 79,443 81,480 88,270 90,792 105,924 113,490 122,220 132,405 151,320 158,886 176,540 211,848 226,980 244,440 264,810 317,772 353,080 397,215 453,960 529,620 635,544 794,430 1,059,240 1,588,860 and 3,177,720, with no remainder.
Since 3,177,720 cannot be divided by just 1 and 3,177,720, it is not a prime number.