A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2621472 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 24 28 32 42 47 48 56 83 84 94 96 112 141 166 168 188 224 249 282 329 332 336 376 498 564 581 658 664 672 752 987 996 1,128 1,162 1,316 1,328 1,504 1,743 1,974 1,992 2,256 2,324 2,632 2,656 3,486 3,901 3,948 3,984 4,512 4,648 5,264 6,972 7,802 7,896 7,968 9,296 10,528 11,703 13,944 15,604 15,792 18,592 23,406 27,307 27,888 31,208 31,584 46,812 54,614 55,776 62,416 81,921 93,624 109,228 124,832 163,842 187,248 218,456 327,684 374,496 436,912 655,368 873,824 1,310,736 and 2,621,472, with no remainder.
Since 2,621,472 cannot be divided by just 1 and 2,621,472, it is not a prime number.