A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1610280 can be evenly divided by 1 2 3 4 5 6 7 8 9 10 12 14 15 18 20 21 24 27 28 30 35 36 40 42 45 54 56 60 63 70 71 72 81 84 90 105 108 120 126 135 140 142 162 168 180 189 210 213 216 252 270 280 284 315 324 355 360 378 405 420 426 497 504 540 567 568 630 639 648 710 756 810 840 852 945 994 1,065 1,080 1,134 1,260 1,278 1,420 1,491 1,512 1,620 1,704 1,890 1,917 1,988 2,130 2,268 2,485 2,520 2,556 2,835 2,840 2,982 3,195 3,240 3,780 3,834 3,976 4,260 4,473 4,536 4,970 5,112 5,670 5,751 5,964 6,390 7,455 7,560 7,668 8,520 8,946 9,585 9,940 11,340 11,502 11,928 12,780 13,419 14,910 15,336 17,892 19,170 19,880 22,365 22,680 23,004 25,560 26,838 28,755 29,820 35,784 38,340 40,257 44,730 46,008 53,676 57,510 59,640 67,095 76,680 80,514 89,460 107,352 115,020 134,190 161,028 178,920 201,285 230,040 268,380 322,056 402,570 536,760 805,140 and 1,610,280, with no remainder.
Since 1,610,280 cannot be divided by just 1 and 1,610,280, it is not a prime number.