A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2636088 can be evenly divided by 1 2 3 4 6 7 8 12 13 14 17 21 24 26 28 34 39 42 51 52 56 68 71 78 84 91 102 104 119 136 142 156 168 182 204 213 221 238 273 284 312 357 364 408 426 442 476 497 546 568 663 714 728 852 884 923 952 994 1,092 1,207 1,326 1,428 1,491 1,547 1,704 1,768 1,846 1,988 2,184 2,414 2,652 2,769 2,856 2,982 3,094 3,621 3,692 3,976 4,641 4,828 5,304 5,538 5,964 6,188 6,461 7,242 7,384 8,449 9,282 9,656 11,076 11,928 12,376 12,922 14,484 15,691 16,898 18,564 19,383 22,152 25,347 25,844 28,968 31,382 33,796 37,128 38,766 47,073 50,694 51,688 62,764 67,592 77,532 94,146 101,388 109,837 125,528 155,064 188,292 202,776 219,674 329,511 376,584 439,348 659,022 878,696 1,318,044 and 2,636,088, with no remainder.
Since 2,636,088 cannot be divided by just 1 and 2,636,088, it is not a prime number.