A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 9786420 can be evenly divided by 1 2 3 4 5 6 7 9 10 12 14 15 18 20 21 27 28 30 35 36 42 45 54 60 63 70 81 84 90 105 108 126 135 140 162 180 189 210 252 270 315 324 378 405 420 540 567 630 756 810 863 945 1,134 1,260 1,620 1,726 1,890 2,268 2,589 2,835 3,452 3,780 4,315 5,178 5,670 6,041 7,767 8,630 10,356 11,340 12,082 12,945 15,534 17,260 18,123 23,301 24,164 25,890 30,205 31,068 36,246 38,835 46,602 51,780 54,369 60,410 69,903 72,492 77,670 90,615 93,204 108,738 116,505 120,820 139,806 155,340 163,107 181,230 217,476 233,010 271,845 279,612 326,214 349,515 362,460 466,020 489,321 543,690 652,428 699,030 815,535 978,642 1,087,380 1,398,060 1,631,070 1,957,284 2,446,605 3,262,140 4,893,210 and 9,786,420, with no remainder.
Since 9,786,420 cannot be divided by just 1 and 9,786,420, it is not a prime number.