A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1809864 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 19 21 24 27 28 36 38 42 49 54 56 57 63 72 76 81 84 98 108 114 126 133 147 152 162 168 171 189 196 216 228 243 252 266 294 324 342 378 392 399 441 456 486 504 513 532 567 588 648 684 756 798 882 931 972 1,026 1,064 1,134 1,176 1,197 1,323 1,368 1,512 1,539 1,596 1,701 1,764 1,862 1,944 2,052 2,268 2,394 2,646 2,793 3,078 3,192 3,402 3,528 3,591 3,724 3,969 4,104 4,536 4,617 4,788 5,292 5,586 6,156 6,804 7,182 7,448 7,938 8,379 9,234 9,576 10,584 10,773 11,172 11,907 12,312 13,608 14,364 15,876 16,758 18,468 21,546 22,344 23,814 25,137 28,728 31,752 32,319 33,516 36,936 43,092 47,628 50,274 64,638 67,032 75,411 86,184 95,256 100,548 129,276 150,822 201,096 226,233 258,552 301,644 452,466 603,288 904,932 and 1,809,864, with no remainder.
Since 1,809,864 cannot be divided by just 1 and 1,809,864, it is not a prime number.