A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 305760 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 49 52 56 60 65 70 78 80 84 91 96 98 104 105 112 120 130 140 147 156 160 168 182 195 196 208 210 224 240 245 260 273 280 294 312 336 364 390 392 416 420 455 480 490 520 546 560 588 624 637 672 728 735 780 784 840 910 980 1,040 1,092 1,120 1,176 1,248 1,274 1,365 1,456 1,470 1,560 1,568 1,680 1,820 1,911 1,960 2,080 2,184 2,352 2,548 2,730 2,912 2,940 3,120 3,185 3,360 3,640 3,822 3,920 4,368 4,704 5,096 5,460 5,880 6,240 6,370 7,280 7,644 7,840 8,736 9,555 10,192 10,920 11,760 12,740 14,560 15,288 19,110 20,384 21,840 23,520 25,480 30,576 38,220 43,680 50,960 61,152 76,440 101,920 152,880 and 305,760, with no remainder.
Since 305,760 cannot be divided by just 1 and 305,760, it is not a prime number.