A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8596588 can be evenly divided by 1 2 4 7 11 13 14 19 22 26 28 38 44 52 76 77 91 113 133 143 154 182 209 226 247 266 286 308 364 418 452 494 532 572 791 836 988 1,001 1,243 1,463 1,469 1,582 1,729 2,002 2,147 2,486 2,717 2,926 2,938 3,164 3,458 4,004 4,294 4,972 5,434 5,852 5,876 6,916 8,588 8,701 10,283 10,868 15,029 16,159 17,402 19,019 20,566 23,617 27,911 30,058 32,318 34,804 38,038 41,132 47,234 55,822 60,116 64,636 76,076 94,468 111,644 113,113 165,319 195,377 226,226 307,021 330,638 390,754 452,452 614,042 661,276 781,508 1,228,084 2,149,147 4,298,294 and 8,596,588, with no remainder.
Since 8,596,588 cannot be divided by just 1 and 8,596,588, it is not a prime number.