A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2550528 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 27 32 36 41 48 54 64 72 81 82 96 108 123 128 144 162 164 192 216 243 246 256 288 324 328 369 384 432 486 492 576 648 656 738 768 864 972 984 1,107 1,152 1,296 1,312 1,476 1,728 1,944 1,968 2,214 2,304 2,592 2,624 2,952 3,321 3,456 3,888 3,936 4,428 5,184 5,248 5,904 6,642 6,912 7,776 7,872 8,856 9,963 10,368 10,496 11,808 13,284 15,552 15,744 17,712 19,926 20,736 23,616 26,568 31,104 31,488 35,424 39,852 47,232 53,136 62,208 70,848 79,704 94,464 106,272 141,696 159,408 212,544 283,392 318,816 425,088 637,632 850,176 1,275,264 and 2,550,528, with no remainder.
Since 2,550,528 cannot be divided by just 1 and 2,550,528, it is not a prime number.