A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 129360 can be evenly divided by 1 2 3 4 5 6 7 8 10 11 12 14 15 16 20 21 22 24 28 30 33 35 40 42 44 48 49 55 56 60 66 70 77 80 84 88 98 105 110 112 120 132 140 147 154 165 168 176 196 210 220 231 240 245 264 280 294 308 330 336 385 392 420 440 462 490 528 539 560 588 616 660 735 770 784 840 880 924 980 1,078 1,155 1,176 1,232 1,320 1,470 1,540 1,617 1,680 1,848 1,960 2,156 2,310 2,352 2,640 2,695 2,940 3,080 3,234 3,696 3,920 4,312 4,620 5,390 5,880 6,160 6,468 8,085 8,624 9,240 10,780 11,760 12,936 16,170 18,480 21,560 25,872 32,340 43,120 64,680 and 129,360, with no remainder.
Since 129,360 cannot be divided by just 1 and 129,360, it is not a prime number.