A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3691968 can be evenly divided by 1 2 3 4 6 7 8 12 14 16 21 24 28 32 41 42 48 56 64 67 82 84 96 112 123 134 164 168 192 201 224 246 268 287 328 336 402 448 469 492 536 574 656 672 804 861 938 984 1,072 1,148 1,312 1,344 1,407 1,608 1,722 1,876 1,968 2,144 2,296 2,624 2,747 2,814 3,216 3,444 3,752 3,936 4,288 4,592 5,494 5,628 6,432 6,888 7,504 7,872 8,241 9,184 10,988 11,256 12,864 13,776 15,008 16,482 18,368 19,229 21,976 22,512 27,552 30,016 32,964 38,458 43,952 45,024 55,104 57,687 65,928 76,916 87,904 90,048 115,374 131,856 153,832 175,808 230,748 263,712 307,664 461,496 527,424 615,328 922,992 1,230,656 1,845,984 and 3,691,968, with no remainder.
Since 3,691,968 cannot be divided by just 1 and 3,691,968, it is not a prime number.