A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1202580 can be evenly divided by 1 2 3 4 5 6 9 10 12 15 17 18 20 27 30 34 36 45 51 54 60 68 85 90 102 108 131 135 153 170 180 204 255 262 270 306 340 393 459 510 524 540 612 655 765 786 918 1,020 1,179 1,310 1,530 1,572 1,836 1,965 2,227 2,295 2,358 2,620 3,060 3,537 3,930 4,454 4,590 4,716 5,895 6,681 7,074 7,860 8,908 9,180 11,135 11,790 13,362 14,148 17,685 20,043 22,270 23,580 26,724 33,405 35,370 40,086 44,540 60,129 66,810 70,740 80,172 100,215 120,258 133,620 200,430 240,516 300,645 400,860 601,290 and 1,202,580, with no remainder.
Since 1,202,580 cannot be divided by just 1 and 1,202,580, it is not a prime number.