A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 6651360 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 30 31 32 36 40 45 48 60 62 72 80 90 93 96 120 124 144 149 155 160 180 186 240 248 279 288 298 310 360 372 447 465 480 496 558 596 620 720 744 745 894 930 992 1,116 1,192 1,240 1,341 1,395 1,440 1,488 1,490 1,788 1,860 2,232 2,235 2,384 2,480 2,682 2,790 2,976 2,980 3,576 3,720 4,464 4,470 4,619 4,768 4,960 5,364 5,580 5,960 6,705 7,152 7,440 8,928 8,940 9,238 10,728 11,160 11,920 13,410 13,857 14,304 14,880 17,880 18,476 21,456 22,320 23,095 23,840 26,820 27,714 35,760 36,952 41,571 42,912 44,640 46,190 53,640 55,428 69,285 71,520 73,904 83,142 92,380 107,280 110,856 138,570 147,808 166,284 184,760 207,855 214,560 221,712 277,140 332,568 369,520 415,710 443,424 554,280 665,136 739,040 831,420 1,108,560 1,330,272 1,662,840 2,217,120 3,325,680 and 6,651,360, with no remainder.
Since 6,651,360 cannot be divided by just 1 and 6,651,360, it is not a prime number.