A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2601312 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 24 28 32 42 48 49 56 79 84 96 98 112 147 158 168 196 224 237 294 316 336 343 392 474 553 588 632 672 686 784 948 1,029 1,106 1,176 1,264 1,372 1,568 1,659 1,896 2,058 2,212 2,352 2,528 2,744 3,318 3,792 3,871 4,116 4,424 4,704 5,488 6,636 7,584 7,742 8,232 8,848 10,976 11,613 13,272 15,484 16,464 17,696 23,226 26,544 27,097 30,968 32,928 46,452 53,088 54,194 61,936 81,291 92,904 108,388 123,872 162,582 185,808 216,776 325,164 371,616 433,552 650,328 867,104 1,300,656 and 2,601,312, with no remainder.
Since 2,601,312 cannot be divided by just 1 and 2,601,312, it is not a prime number.