A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 5911500 can be evenly divided by 1 2 3 4 5 6 7 10 12 14 15 20 21 25 28 30 35 42 50 60 70 75 84 100 105 125 140 150 175 210 250 300 350 375 420 500 525 563 700 750 875 1,050 1,126 1,500 1,689 1,750 2,100 2,252 2,625 2,815 3,378 3,500 3,941 5,250 5,630 6,756 7,882 8,445 10,500 11,260 11,823 14,075 15,764 16,890 19,705 23,646 28,150 33,780 39,410 42,225 47,292 56,300 59,115 70,375 78,820 84,450 98,525 118,230 140,750 168,900 197,050 211,125 236,460 281,500 295,575 394,100 422,250 492,625 591,150 844,500 985,250 1,182,300 1,477,875 1,970,500 2,955,750 and 5,911,500, with no remainder.
Since 5,911,500 cannot be divided by just 1 and 5,911,500, it is not a prime number.