A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 87360 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 13 14 15 16 20 21 24 26 28 30 32 35 39 40 42 48 52 56 60 64 65 70 78 80 84 91 96 104 105 112 120 130 140 156 160 168 182 192 195 208 210 224 240 260 273 280 312 320 336 364 390 416 420 448 455 480 520 546 560 624 672 728 780 832 840 910 960 1,040 1,092 1,120 1,248 1,344 1,365 1,456 1,560 1,680 1,820 2,080 2,184 2,240 2,496 2,730 2,912 3,120 3,360 3,640 4,160 4,368 5,460 5,824 6,240 6,720 7,280 8,736 10,920 12,480 14,560 17,472 21,840 29,120 43,680 and 87,360, with no remainder.
Since 87,360 cannot be divided by just 1 and 87,360, it is not a prime number.