4,294,967,297

Number
$4 \, 294 \, 967 \, 297$ is:


 * $641 \times 6 \, 700 \, 417$


 * The $6$th Fermat number after $3, 5, 17, 257, 65 \, 537$:
 * $4 \, 294 \, 967 \, 297 = 2^{\left({2^5}\right)} + 1 = 2^{32} + 1$
 * and the $1$st not to be prime.