A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 171360 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 16 17 18 20 21 24 28 30 32 34 35 36 40 42 45 48 51 56 60 63 68 70 72 80 84 85 90 96 102 105 112 119 120 126 136 140 144 153 160 168 170 180 204 210 224 238 240 252 255 272 280 288 306 315 336 340 357 360 408 420 476 480 504 510 544 560 595 612 630 672 680 714 720 765 816 840 952 1,008 1,020 1,071 1,120 1,190 1,224 1,260 1,360 1,428 1,440 1,530 1,632 1,680 1,785 1,904 2,016 2,040 2,142 2,380 2,448 2,520 2,720 2,856 3,060 3,360 3,570 3,808 4,080 4,284 4,760 4,896 5,040 5,355 5,712 6,120 7,140 8,160 8,568 9,520 10,080 10,710 11,424 12,240 14,280 17,136 19,040 21,420 24,480 28,560 34,272 42,840 57,120 85,680 and 171,360, with no remainder.
Since 171,360 cannot be divided by just 1 and 171,360, it is not a prime number.