A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 585480 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 17 20 21 24 28 30 34 35 40 41 42 51 56 60 68 70 82 84 85 102 105 119 120 123 136 140 164 168 170 204 205 210 238 246 255 280 287 328 340 357 408 410 420 476 492 510 574 595 615 680 697 714 820 840 861 952 984 1,020 1,148 1,190 1,230 1,394 1,428 1,435 1,640 1,722 1,785 2,040 2,091 2,296 2,380 2,460 2,788 2,856 2,870 3,444 3,485 3,570 4,182 4,305 4,760 4,879 4,920 5,576 5,740 6,888 6,970 7,140 8,364 8,610 9,758 10,455 11,480 13,940 14,280 14,637 16,728 17,220 19,516 20,910 24,395 27,880 29,274 34,440 39,032 41,820 48,790 58,548 73,185 83,640 97,580 117,096 146,370 195,160 292,740 and 585,480, with no remainder.
Since 585,480 cannot be divided by just 1 and 585,480, it is not a prime number.