A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1328580 can be evenly divided by 1 2 3 4 5 6 9 10 11 12 15 18 20 22 30 33 36 44 45 55 60 61 66 90 99 110 121 122 132 165 180 183 198 220 242 244 305 330 363 366 396 484 495 549 605 610 660 671 726 732 915 990 1,089 1,098 1,210 1,220 1,342 1,452 1,815 1,830 1,980 2,013 2,178 2,196 2,420 2,684 2,745 3,355 3,630 3,660 4,026 4,356 5,445 5,490 6,039 6,710 7,260 7,381 8,052 10,065 10,890 10,980 12,078 13,420 14,762 20,130 21,780 22,143 24,156 29,524 30,195 36,905 40,260 44,286 60,390 66,429 73,810 88,572 110,715 120,780 132,858 147,620 221,430 265,716 332,145 442,860 664,290 and 1,328,580, with no remainder.
Since 1,328,580 cannot be divided by just 1 and 1,328,580, it is not a prime number.