A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8601376 can be evenly divided by 1 2 4 7 8 14 16 19 28 32 38 43 47 56 76 86 94 112 133 152 172 188 224 266 301 304 329 344 376 532 602 608 658 688 752 817 893 1,064 1,204 1,316 1,376 1,504 1,634 1,786 2,021 2,128 2,408 2,632 3,268 3,572 4,042 4,256 4,816 5,264 5,719 6,251 6,536 7,144 8,084 9,632 10,528 11,438 12,502 13,072 14,147 14,288 16,168 22,876 25,004 26,144 28,294 28,576 32,336 38,399 45,752 50,008 56,588 64,672 76,798 91,504 100,016 113,176 153,596 183,008 200,032 226,352 268,793 307,192 452,704 537,586 614,384 1,075,172 1,228,768 2,150,344 4,300,688 and 8,601,376, with no remainder.
Since 8,601,376 cannot be divided by just 1 and 8,601,376, it is not a prime number.