A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 2141856 can be evenly divided by 1 2 3 4 6 8 9 12 16 18 24 27 32 36 37 48 54 67 72 74 96 108 111 134 144 148 201 216 222 268 288 296 333 402 432 444 536 592 603 666 804 864 888 999 1,072 1,184 1,206 1,332 1,608 1,776 1,809 1,998 2,144 2,412 2,479 2,664 3,216 3,552 3,618 3,996 4,824 4,958 5,328 6,432 7,236 7,437 7,992 9,648 9,916 10,656 14,472 14,874 15,984 19,296 19,832 22,311 28,944 29,748 31,968 39,664 44,622 57,888 59,496 66,933 79,328 89,244 118,992 133,866 178,488 237,984 267,732 356,976 535,464 713,952 1,070,928 and 2,141,856, with no remainder.
Since 2,141,856 cannot be divided by just 1 and 2,141,856, it is not a prime number.