A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7716280 can be evenly divided by 1 2 4 5 8 10 11 13 19 20 22 26 38 40 44 52 55 65 71 76 88 95 104 110 130 142 143 152 190 209 220 247 260 284 286 355 380 418 440 494 520 568 572 710 715 760 781 836 923 988 1,045 1,144 1,235 1,349 1,420 1,430 1,562 1,672 1,846 1,976 2,090 2,470 2,698 2,717 2,840 2,860 3,124 3,692 3,905 4,180 4,615 4,940 5,396 5,434 5,720 6,248 6,745 7,384 7,810 8,360 9,230 9,880 10,153 10,792 10,868 13,490 13,585 14,839 15,620 17,537 18,460 20,306 21,736 26,980 27,170 29,678 31,240 35,074 36,920 40,612 50,765 53,960 54,340 59,356 70,148 74,195 81,224 87,685 101,530 108,680 118,712 140,296 148,390 175,370 192,907 203,060 296,780 350,740 385,814 406,120 593,560 701,480 771,628 964,535 1,543,256 1,929,070 3,858,140 and 7,716,280, with no remainder.
Since 7,716,280 cannot be divided by just 1 and 7,716,280, it is not a prime number.