A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1859520 can be evenly divided by 1 2 3 4 5 6 8 10 12 13 15 16 20 24 26 30 32 39 40 48 52 60 64 65 78 80 96 104 120 130 149 156 160 192 195 208 240 260 298 312 320 390 416 447 480 520 596 624 745 780 832 894 960 1,040 1,192 1,248 1,490 1,560 1,788 1,937 2,080 2,235 2,384 2,496 2,980 3,120 3,576 3,874 4,160 4,470 4,768 5,811 5,960 6,240 7,152 7,748 8,940 9,536 9,685 11,622 11,920 12,480 14,304 15,496 17,880 19,370 23,244 23,840 28,608 29,055 30,992 35,760 38,740 46,488 47,680 58,110 61,984 71,520 77,480 92,976 116,220 123,968 143,040 154,960 185,952 232,440 309,920 371,904 464,880 619,840 929,760 and 1,859,520, with no remainder.
Since 1,859,520 cannot be divided by just 1 and 1,859,520, it is not a prime number.