A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8506596 can be evenly divided by 1 2 3 4 6 7 12 14 17 21 23 28 34 37 42 46 49 51 68 69 74 84 92 98 102 111 119 138 147 148 161 196 204 222 238 259 276 294 322 357 391 444 476 483 518 588 629 644 714 777 782 833 851 966 1,036 1,127 1,173 1,258 1,428 1,554 1,564 1,666 1,702 1,813 1,887 1,932 2,254 2,346 2,499 2,516 2,553 2,737 3,108 3,332 3,381 3,404 3,626 3,774 4,403 4,508 4,692 4,998 5,106 5,439 5,474 5,957 6,762 7,252 7,548 8,211 8,806 9,996 10,212 10,878 10,948 11,914 13,209 13,524 14,467 16,422 17,612 17,871 19,159 21,756 23,828 26,418 28,934 30,821 32,844 35,742 38,318 41,699 43,401 52,836 57,477 57,868 61,642 71,484 76,636 83,398 86,802 92,463 101,269 114,954 123,284 125,097 166,796 173,604 184,926 202,538 229,908 250,194 303,807 369,852 405,076 500,388 607,614 708,883 1,215,228 1,417,766 2,126,649 2,835,532 4,253,298 and 8,506,596, with no remainder.
Since 8,506,596 cannot be divided by just 1 and 8,506,596, it is not a prime number.