A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3204768 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 19 21 24 28 32 38 42 48 56 57 76 84 96 112 114 133 152 168 224 228 251 266 304 336 399 456 502 532 608 672 753 798 912 1,004 1,064 1,506 1,596 1,757 1,824 2,008 2,128 3,012 3,192 3,514 4,016 4,256 4,769 5,271 6,024 6,384 7,028 8,032 9,538 10,542 12,048 12,768 14,056 14,307 19,076 21,084 24,096 28,112 28,614 33,383 38,152 42,168 56,224 57,228 66,766 76,304 84,336 100,149 114,456 133,532 152,608 168,672 200,298 228,912 267,064 400,596 457,824 534,128 801,192 1,068,256 1,602,384 and 3,204,768, with no remainder.
Since 3,204,768 cannot be divided by just 1 and 3,204,768, it is not a prime number.