A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8540784 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 28 36 37 42 48 56 63 72 74 84 111 112 126 144 148 168 222 229 252 259 296 333 336 444 458 504 518 592 666 687 777 888 916 1,008 1,036 1,332 1,374 1,554 1,603 1,776 1,832 2,061 2,072 2,331 2,664 2,748 3,108 3,206 3,664 4,122 4,144 4,662 4,809 5,328 5,496 6,216 6,412 8,244 8,473 9,324 9,618 10,992 12,432 12,824 14,427 16,488 16,946 18,648 19,236 25,419 25,648 28,854 32,976 33,892 37,296 38,472 50,838 57,708 59,311 67,784 76,257 76,944 101,676 115,416 118,622 135,568 152,514 177,933 203,352 230,832 237,244 305,028 355,866 406,704 474,488 533,799 610,056 711,732 948,976 1,067,598 1,220,112 1,423,464 2,135,196 2,846,928 4,270,392 and 8,540,784, with no remainder.
Since 8,540,784 cannot be divided by just 1 and 8,540,784, it is not a prime number.