A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5263776 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 16 18 21 24 28 32 36 42 48 49 56 63 72 84 96 98 112 126 144 147 168 196 224 252 288 294 336 373 392 441 504 588 672 746 784 882 1,008 1,119 1,176 1,492 1,568 1,764 2,016 2,238 2,352 2,611 2,984 3,357 3,528 4,476 4,704 5,222 5,968 6,714 7,056 7,833 8,952 10,444 11,936 13,428 14,112 15,666 17,904 18,277 20,888 23,499 26,856 31,332 35,808 36,554 41,776 46,998 53,712 54,831 62,664 73,108 83,552 93,996 107,424 109,662 125,328 146,216 164,493 187,992 219,324 250,656 292,432 328,986 375,984 438,648 584,864 657,972 751,968 877,296 1,315,944 1,754,592 2,631,888 and 5,263,776, with no remainder.
Since 5,263,776 cannot be divided by just 1 and 5,263,776, it is not a prime number.