A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8558880 can be evenly divided by 1 2 3 4 5 6 8 10 11 12 15 16 20 22 24 30 32 33 40 44 48 55 60 66 80 88 96 110 120 132 160 165 176 220 240 264 330 352 440 480 528 660 880 1,056 1,320 1,621 1,760 2,640 3,242 4,863 5,280 6,484 8,105 9,726 12,968 16,210 17,831 19,452 24,315 25,936 32,420 35,662 38,904 48,630 51,872 53,493 64,840 71,324 77,808 89,155 97,260 106,986 129,680 142,648 155,616 178,310 194,520 213,972 259,360 267,465 285,296 356,620 389,040 427,944 534,930 570,592 713,240 778,080 855,888 1,069,860 1,426,480 1,711,776 2,139,720 2,852,960 4,279,440 and 8,558,880, with no remainder.
Since 8,558,880 cannot be divided by just 1 and 8,558,880, it is not a prime number.