A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1600632 can be evenly divided by 1 2 3 4 6 8 9 11 12 18 22 24 33 36 43 44 47 66 72 86 88 94 99 129 132 141 172 188 198 258 264 282 344 376 387 396 423 473 516 517 564 774 792 846 946 1,032 1,034 1,128 1,419 1,548 1,551 1,692 1,892 2,021 2,068 2,838 3,096 3,102 3,384 3,784 4,042 4,136 4,257 4,653 5,676 6,063 6,204 8,084 8,514 9,306 11,352 12,126 12,408 16,168 17,028 18,189 18,612 22,231 24,252 34,056 36,378 37,224 44,462 48,504 66,693 72,756 88,924 133,386 145,512 177,848 200,079 266,772 400,158 533,544 800,316 and 1,600,632, with no remainder.
Since 1,600,632 cannot be divided by just 1 and 1,600,632, it is not a prime number.