A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2655936 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 27 29 32 36 48 53 54 58 64 72 87 96 106 108 116 144 159 174 192 212 216 232 261 288 318 348 424 432 464 477 522 576 636 696 783 848 864 928 954 1,044 1,272 1,392 1,431 1,537 1,566 1,696 1,728 1,856 1,908 2,088 2,544 2,784 2,862 3,074 3,132 3,392 3,816 4,176 4,611 5,088 5,568 5,724 6,148 6,264 7,632 8,352 9,222 10,176 11,448 12,296 12,528 13,833 15,264 16,704 18,444 22,896 24,592 25,056 27,666 30,528 36,888 41,499 45,792 49,184 50,112 55,332 73,776 82,998 91,584 98,368 110,664 147,552 165,996 221,328 295,104 331,992 442,656 663,984 885,312 1,327,968 and 2,655,936, with no remainder.
Since 2,655,936 cannot be divided by just 1 and 2,655,936, it is not a prime number.