A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 816270 can be evenly divided by 1 2 3 5 6 7 10 13 14 15 21 23 26 30 35 39 42 46 65 69 70 78 91 105 115 130 138 161 169 182 195 210 230 273 299 322 338 345 390 455 483 507 546 598 690 805 845 897 910 966 1,014 1,183 1,365 1,495 1,610 1,690 1,794 2,093 2,366 2,415 2,535 2,730 2,990 3,549 3,887 4,186 4,485 4,830 5,070 5,915 6,279 7,098 7,774 8,970 10,465 11,661 11,830 12,558 17,745 19,435 20,930 23,322 27,209 31,395 35,490 38,870 54,418 58,305 62,790 81,627 116,610 136,045 163,254 272,090 408,135 and 816,270, with no remainder.
Since 816,270 cannot be divided by just 1 and 816,270, it is not a prime number.